Carl M. Shoffler, 51, a Prince George's County fire official and former D.C. police undercover detective who became a legend among observers and peers for his investigations of everything from organized crime to the Watergate break-in, died of pancreatitis July 13 at Johns Hopkins Hospital in Baltimore.

The 20-year police veteran was involved in the kinds of cases they make into movies. The cases included terrorist acts, hate crimes and investigations of political extremist groups. He was called a master of disguise, a detective with an enormously wide range of sources and informants and an authority on criminal psychology.

Although he was widely known in the law enforcement community, his work, by its nature, kept him largely out of the public eye. But that changed in 1972, when a series of serendipitous accidents resulted in his taking part in the arrest of five people in the most famous "third-rate burglary" in U.S. history.

At 1:52 a.m. on June 17, 1972, he and two other plainclothes officers had just driven under the Whitehurst Freeway on their way to Georgetown when a dispatcher alerted them to a "door's open" call at the Watergate office complex and asked them to check for a possible robbery.

The officers, who were going off duty, agreed to investigate. A marked police cruiser, which initially had been dispatched to the scene, had run out of gas. The officers met with a Watergate security guard, who told them of his suspicions of burglars. The detectives eventually found themselves in the offices of the Democratic National Committee and were the captors of five men who would become known as the Watergate burglars.

The burglars, whose crimes eventually were linked to the Republican White House of Richard M. Nixon, had thought they were protected by a lookout in the Howard Johnson Motor Lodge across from the Watergate. But the appearance of the scruffy "casual clothes" detectives in their battered, unmarked car did not raise suspicions. The Watergate burglars were not warned in time to flee the building.

The lookout was spotted by Mr. Shoffler while he was crawling, with gun in hand, along a building ledge. The detectives booked their captives at 2nd District police headquarters, and by that time, they had become more than a little suspicious.

The burglars seemed too neatly attired, in jackets and ties, to be typical criminals, and the fact that they casually waived their rights to attorneys only heightened suspicions. The burglars, who had carefully prepared false identities for just such an emergency, then suffered a setback when two of them became confused and claimed to be the same person. It was the first thread to unravel in a drama that lasted until Nixon resigned as president in 1974.

Long before Watergate, Mr. Shoffler had gained the trust and admiration of many officers, reporters and even criminals. After learning of the detective's death, former police colleagues recalled him as a master of interrogation and criminal psychology. Colleagues and observers said his ability to get a confession or gain a valuable piece of information had to do with his quiet honesty and an ability to understand the intent of ideologically motivated criminals rather than trickery or threats.

He also was described as a dogged and determined officer who was proud of working an "11-day week" and of relentlessly continuing a hunt when others had given up.

That might be illustrated by his dealings with Daoud Salahuddin. Salahuddin, born as David Belfield, was a college student, martial arts expert and Shiite Muslim. Federal and local authorities are convinced that in 1980, Salahuddin, posing as a postal carrier, shot and killed Ali Akbar Tabatabai in the victim's Bethesda home. A press officer in the Iranian Embassy in Washington during the reign of the shah, Tabatabai had become a leading critic of the Ayatollah Ruhollah Khomeini.

Salahuddin escaped to Iran, beyond the reach of U.S. law. Mr. Shoffler served on the task force that assisted Montgomery County police in the case and, through his sources, made contact with Salahuddin. A former reporter said that while other authorities were treating Salahuddin as a murderer and a terrorist, Mr. Shoffler was speaking with him on the phone, attempting to persuade him to return and treating him as a "revolutionary soldier." Only recently, Salahuddin is said to have called to check on Mr. Shoffler's health and wish him well.

Mr. Shoffler, who lived in Bowie, was a native of Ashland, Pa. He served in the Army in the mid- to late 1960s, including tours with the Army Security Agency and in Vietnam. He attended American University and Prince George's Community College.

He served with the D.C. police, mainly as a detective in its criminal intelligence unit, from 1969 to 1989. He then joined the Prince George's County Fire Department, where he was a fire investigator and chief intelligence investigator at the time of his death.

Mr. Shoffler was a charter member of the Combined Law Enforcement Intelligence Group and was certified as a polygraph expert. He was a member of the D.C. Fraternal Order of Police, the D.C. Retired Detectives Association and the Maryland Arson Association.

For more than 20 years, he coached a variety of Bowie community athletic teams including football and girls softball. He also had coached at Bowie and Eleanor Roosevelt high schools and at Riverdale Baptist School.

Survivors include his wife of 30 years, Helen Elizabeth Boyd Shoffler of Bowie; three children, Karl Shawn Shoffler of Laurel, Loren Allen Shoffler of Berlin, Md., and Michelle Scarlett Shoffler of Bowie; and his parents, Allen and Eleanor Shoffler, a brother, David, and two sisters, Barbara Hoover and Fay Fausnaught, all of Pennsylvania.

Carl M. Shoffler, one of three Washington policemen whose arrest of five burglars 24 years ago touched off the Watergate scandals and ultimately brought down a Presidency, died on Saturday at Johns Hopkins Hospital in Baltimore. He was 51 and lived in Bowie, Md. The cause was pancreatitis.

Mr. Shoffler, another plainclothes officer and a police sergeant were not far from the Watergate hotel and office complex in Washington early on June 17, 1972, when they received a report that a door had been found open at the Democratic National Committee's offices there.

Arriving at the scene, they discovered five men trying to burglarize and wiretap the Democratic offices, in what was later found to be part of a pattern of Republican political espionage.

The five men seized at the Watergate were Bernard L. Barker, Virgilio R. Gonzalez, Eugenio R. Martinez, James W. McCord Jr. and Frank A. Sturgis. They and two other men -- E. Howard Hunt Jr. and G. Gordon Liddy -- all either pleaded guilty or were convicted at trial in connection with the break-in, and all, it turned out, had been working, directly or indirectly, for President Richard M. Nixon's re-election campaign committee.

Mr. Nixon easily won re-election in November 1972. But the ever widening scandals from which the Watergate arrests proceeded, largely involving Administration efforts to keep the burglars silent about their ties to the White House, ultimately led him to resign in 1974, the only United States President to do so.

Mr. Shoffler was apparently the right officer to handle the Watergate arrests. As National Review put it in a 1992 article: "When Watergate burglar Eugenio Martinez and his team were apprehended, Martinez struggled with arresting officer Carl Shoffler to conceal something on his person. Shoffler wrestled from him a key, which the F.B.I. identified as fitting the desk of Ida Wells," a member of the Democratic National Committee staff.

And in a 1976 book, Sam Dash, who had been chief counsel to the Senate Watergate committee, described Mr. Shoffler as one of "the foundation-laying witnesses" at the committee's hearings, which found a broad pattern of White House wrongdoing.

But if Mr. Shoffler played a leading role in Watergate's opening act, "he never bragged about it," Detective Ronald Robertson, chairman of the Washington police officers' and sergeants' union, said yesterday.

"He just did his job," Detective Robertson said, "and went quietly on his way. I don't think it changed his life one bit."

Mr. Shoffler, a native of Ashland, Pa., attended American University in Washington, spent four years in the Army, including a tour in Vietnam, and then joined the Washington police force in 1969. He became a detective and spent 16 years in the department's intelligence unit before retiring with a pension in 1989. Then he became an investigator for the Fire Department of Prince Georges County, Md. At his death, his title there was chief intelligence investigator.

He is survived by his wife of three decades, Helen Elizabeth Boyd Shoffler; three children, Karl Shawn Shoffler of Laurel, Md., Loren Allen Shoffler of Berlin, Md., and Michelle Scarlett Shoffler of Bowie; his parents, Allen and Eleanor Shoffler, who live in Pennsylvania; two sisters, Barbara Hoover and Fay Fausnaught, both of Pennsylvania, and a brother, David, also of Pennsylvania.

Other cops call their informants snitches or stoolies, and often treat them with contempt. Carl Shoffler, the legendary Washington, D.C., police intelligence detective, who died on July 13th, called them "sources" and, sometimes, friends. He gave out his home telephone number to mobsters on the run, to suspected terrorists, and to defectors from hate groups. For most people engaged in police work, especially those devoted to their families, such a practice would be unthinkable. But for Shoffler it was a way to build trust. He needed those unsavory informants; he didn't coddle them, but they knew that he would always be up front and straight with them.

In 1982, Shoffier and another detective, Michael Hubbard, wrote a confidential police memorandum that would eventually cause havoc in D.C. The detectives had found three reliable informants who were ready to testify before a grand jury that they had witnessed the mayor, Marion Barry, snorting cocaine at a private party in a strip club. A copy of their memo was hand-carried to the U.S. Department of Justice. To Shoffier and Hubbard's bewilderment, little action was taken on Barry's case until 1990, when F.B.I. agents videotaped him in a hotel room with a former model and arrested him for cocaine possession. He was later convicted and sent to prison for six months.

When Shoffler was stricken with pancreatitis last month, among the first to call his wife with words of comfort was a fugitive wanted for murder. "This is Daoud," he said, and Helene Shoffler knew at once that it was David Belfield, now known as Daoud Salahuddin, a former Howard University student and Muslim militant wanted for the 1980 assassination of a onetime press officer for the Iranian Embassy. Until Shoffier fell ill, he was trying to arrange Belfield's surrender. To elude a worldwide F.B.I. manhunt, Belfield had taken refuge in paramilitary training camps in Iran, Afghanistan, and Lebanon. He was in deep cover, but Shoffler, working his sources, had somehow managed to make contact. The fugitive and the detective talked frequently; Shoffler even got Belfield to agree to a television interview earlier this year in which he admitted that he was indeed the triggerman in the 1980 assassination.

One of Shoifier's favorite sources was a former Mob strong-arm man who worked undercover to penetrate a Mafia loan-sharking ring that targeted government employees. When the source, who is now in hiding, learned that Shoffler had died, he sobbed uncontrollably. "I owe my life to this man," the former mobster said. "My family owes him everything. What do I do now?"

Shoffler put together the informants, cops, federal agents, and investigative strategies that led to the closing of dozens of major cases. His style was stealth. The one time he was not able to avoid the limelight was in the early morning of June 17, 1972. It was his twenty-seventh birthday, and Shoffler was working undercover with two other policemen in an unmarked car when a dispatcher asked them to check out a possible burglary in progress at the Watergate office complex. When Shoffier and the other cops arrived at the offices of the Democratic National Committee, they made the arrests that eventually led to the resignation of President Nixon.

Among the tributes to Carl Shoffler last week was this: "He always told the truth and let the chips fall where they may. You cannot ask more of a man or a law-enforcement officer." The words came from G. Gordon Liddy, the man who plotted the Watergate burglary. Years after the burglary, the arresting officer and the toughest bird in the whole Watergate scandal became unlikely buddies.