John J. Caulfield, a security operative who was responsible for wiretaps and other so-called “dirty tricks” of the Nixon White House, and who offered executive clemency to a convicted Watergate burglar, died June 17 in Vero Beach, Fla. He was 83.

A funeral home in Vero Beach confirmed his death, but the cause could not be learned.

Mr. Caulfield, who was often known as Jack, was a burly onetime New York City police officer who entered the orbit of Richard M. Nixon as a chief of security during the 1968 presidential campaign. After Nixon was elected, Mr. Caulfield assumed a vaguely defined role as a White House staff assistant, with responsibilities that ranged from bodyguard to collector of intelligence.

He was linked to several operations that skirted beyond the edge of legality, including wiretapping, pressure on the Internal Revenue Service and the planned bombing of a Washington think tank. But Mr. Caulfield was best known as the White House official who extended an offer of clemency, cash and future employment to James W. McCord Jr. if McCord, a convicted Watergate burglar, refused to testify against members of Nixon’s inner circle.

McCord revealed Mr. Caulfield’s offer at a Senate Watergate hearing in May 1973. It was the first evidence that appeared to link Nixon directly with the Watergate burglary and the subsequent coverup.

McCord said Mr. Caulfield invoked the president’s name while making the offer during a meeting in January 1973 at an overlook on the George Washington Parkway. In testimony to the Senate committee, Mr. Caulfield said Nixon “probably did know” that McCord had been offered clemency in return for his silence.

Later, Mr. Caulfield said he believed the scheme came from his onetime boss, White House counsel John Dean, and that Nixon may not have authorized it.

“I know when wrongdoing is occurring,” Mr. Caulfield said in 1973, under questioning from Sen. Lowell P. Weicker Jr. (R-Conn.). “I have indicated here that I knew that the offer of executive clemency in this matter was wrong, yes sir, I knew that. But what I am saying to you, sir, is that my loyalties, especially to the president of the United States, overrided those considerations.”

Mr. Caulfield left the White House several months before the Watergate break-in occurred in June 1972 and was never prosecuted. But his Senate testimony did include some jaw-dropping revelations about the Nixon White House’s intelligence-gathering efforts.

Among other things, he revealed that the president’s brother, Donald Nixon, was under surveillance by the Secret Service and had a wiretap on his telephone.

In 1969, when Mary Jo Kopechne died in a car driven by Sen. Edward M. Kennedy (D-Mass.) on Chappaquiddick Island, Mass., one of Mr. Caulfield’s White House assistants was among the first people on the scene to interview witnesses.

Mr. Caulfield reportedly ordered tax audits and wiretaps of journalists, and he approached the IRS to quash criminal prosecutions against Nixon’s supporters in California. White House adviser Charles Colson — who died April 21 — once suggested that Mr. Caulfield and his subordinates firebomb the Brookings Institution, a liberal-leaning think tank, but the idea was abandoned.

G. Gordon Liddy, a convicted Watergate conspirator, wrote in his 1996 autobiography that Mr. Caulfield had “obtained” the appointment book of Xaviera Hollander, a 1970s madam and writer known as the “Happy Hooker.” The entries, however, “were useless to either Democrats or Republicans because so many prominent members of both parties were represented in them they would cancel each other out in a political ‘balance of terror.’ ”

John James Caulfield, the son of Irish immigrants, was born March 12, 1929, in the Bronx. He attended Wake Forest University in North Carolina for two years on a basketball scholarship, served in the Army during the Korean War before joining the New York Police Department in 1953.

He served in the department’s special services bureau from 1956 to 1966, guarding dignitaries and conducting undercover operations. He was working as a homicide detective when he took a leave of absence to help with security during Nixon’s 1968 presidential campaign.

One of his duties in the White House was to guard Attorney General John Mitchell, but Mitchell lost confidence in Mr. Caulfield during a trip to Florida. According to James Rosen’s “The Strong Man: John Mitchell and the Secrets of Watergate” (2008), once the plane landed in Miami, Mr. Caulfield realized he had left his gun in a lounge at National Airport.

“That was the end of Caulfield, as far as I was concerned,” Mitchell said.

Mr. Caulfield’s first marriage, to Marjorie Caulfield, ended in divorce. Survivors include his wife of 20 years, Nancy E. Caulfield of Vero Beach; three sons from his first marriage; and nine grandchildren.

After the White House, Mr. Caulfield briefly supervised the special agents of the Bureau of Alcohol, Tobacco and Firearms. Before moving to Florida in 1988, he was an executive for a New York aerosol business run by Robert H. Abplanalp, one of Nixon’s closest friends.