Robert C. Mardian, 82, the attorney for President Richard Nixon’s Committee to Re-Elect the President whose conviction of conspiracy to obstruct justice in the Watergate scandal was overturned on appeal, died of lung cancer July 17 at his vacation home in San Clemente, Calif.

Mr. Mardian, a former assistant attorney general, consistently denied that he was involved in Nixon administration attempts to cover up its involvement in the break-in and attempted bugging of the Democratic National Headquarters office at the Watergate complex June 17, 1972. He was assigned to handle the legal issues growing out of the break-in, he testified during his 1974 trial, but he said he didn’t know about the break-in before it happened. He also testified that former attorney general John N. Mitchell admitted approving a $250,000 budget for G. Gordon Liddy, who led the team of burglars.

Mr. Mardian testified that he was golfing on the West Coast when he learned of the break-in from Nixon’s campaign aide, Jeb Stuart Magruder. According to his testimony, he told Magruder: “Burglary is bad enough. You might get away with it -- boys will be boys. But bugging is disastrous.”

Others testified that he was key in getting the Watergate burglars released from jail before it was discovered how deeply the administration was involved in the crime, but Mr. Mardian said that was impossible, given his location and the difference in time zones.

Mr. Mardian was sentenced to 10 months to three years on a single count of conspiracy. In the same trial, Mitchell and White House aides John Ehrlichman and H.R. Haldeman were also convicted. Another campaign attorney, Kenneth W. Parkinson, was acquitted.

Mr. Mardian, a balding, gravel-voiced and dour-faced man, had unsuccessfully tried to avoid testifying at the trial on the grounds of attorney-client privilege. Upon the verdict, The Washington Post reported that he “seemed stunned. . . . Mardian seemed devastated by the jury verdict against him and sat glued to his seat in the courtroom until it was almost empty, apparently trying to compose himself.”

The U.S. Court of Appeals in 1976 said Mr. Mardian should have been given a separate trial because his attorney of first choice became ill after the trial began and because of his more limited role in the crime. Rather than retrying him, the special prosecutor dropped the charge.

By late 1972, he had left public life, and except for his trial and an appearance at Mitchell’s funeral in 1988, he had mostly stayed out of the spotlight since.

Mr. Mardian had been a powerful figure in Washington, described at the time as “one of the most visible and vocal spokesmen for law and order” in the Nixon administration. “You talk of wearing flags in lapels -- this guy would have sewn a flag on his back if they’d let him,” a Justice Department colleague told The Post in 1973.

At the Justice Department, he was in charge of reviving the Internal Security Division, which tapped phones of reporters and launched investigations of alleged subversives. He also led the probe of the leak and publication of the top-secret history of the Vietnam War known as the Pentagon Papers.

The FBI, in a two-year probe of the leak, had surreptitiously tape recorded reporters, White House aides and others. Mr. Mardian had custody of transcripts of those tapes, and he passed them along to Ehrlichman in the White House. The transcripts later went missing.

Mr. Mardian told the Senate Select Watergate Committee in 1973 that four days after the Watergate burglary, Liddy told him that he was acting on the “express authority of the president of the United States with the assistance of the Central Intelligence Agency.” That was the first time, Mr. Mardian said, that he learned of the break-in at the office of Daniel Ellsberg’s psychiatrist.

Ellsberg leaked the Pentagon Papers to the New York Times, The Washington Post and other newspapers, and the federal investigation of that leak is generally regarded as the start of the Nixon administration’s abuses of power.

Mr. Mardian told the Senate committee that he learned the day after the Watergate break-in that there was a budget for “dirty tricks and black advance,” but he didn’t understand that “black advance” meant an attempt to disrupt the advance operations of political opponents.

Mr. Mardian was born in Pasadena, Calif., the youngest son of Armenian immigrants. He attended the University of California at Santa Barbara, but his studies were interrupted by World War II. He served in the Navy, assigned to a sub-chaser in the Aleutian Islands. After the war, he graduated from the University of Southern California Law School in 1949.

He went into the private practice of law in Pasadena, later joining Wesco Financial Corp., and was executive vice president and general counsel for its subsidiary, Mutual Savings and Loan Association, from 1962 to 1969.

He served as western regional director for Sen. Barry Goldwater’s presidential campaign in 1964 and was chairman of Ronald Reagan’s state advisory committee during his 1966 California gubernatorial campaign. In 1968, he became western states co-chairman for Nixon’s presidential campaign.

After Nixon took office in 1969, Mr. Mardian became general counsel to the Department of Health, Education and Welfare. In 1970, he was appointed by Nixon as executive director of the Cabinet Committee on Education after he wrote a memo to the HEW secretary suggesting that school desegregation guidelines be relaxed but not announced publicly. His suggestion was not taken. Later in 1970, Mr. Mardian was confirmed by the Senate as an assistant attorney general.

In April 1972, Mr. Mardian became the attorney for the Committee to Re-Elect the President and became embroiled in the Watergate scandal. He left government work in November 1972, moving to Phoenix to join his brothers in the family construction business. He retired in 2002 and resided there, with a summer home in California.

A year ago, he told the Arizona Republic that he was shocked by news that W. Mark Felt, the second-in-command of the FBI, was Deep Throat, the secret source of Washington Post reporter Bob Woodward. Felt “betrayed his position,” Mr. Mardian told the Phoenix newspaper.

“He was in a position of authority at the FBI, investigating a matter, and the last thing in the world he should be doing is giving information to a newspaper,” Mr. Mardian was quoted as saying. “I just can’t imagine him doing what he did. He’s the last person in the world who should have brought it to light.”

Survivors include his wife of 60 years, Dorothy Mardian of Phoenix; three sons, Robert C. Mardian Jr. of Dana Point, Calif., William D. Mardian of San Clemente and Blair A. Mardian of Kona, Hawaii; two brothers; a sister; and 10 grandchildren.