James D. St. Clair, 80, a pillar of the Boston bar who made notable appearances before Congress and the federal courts in an effort to save President Richard M. Nixon from the scandal of Watergate, died March 10 at a nursing home in Westwood, Mass. Death followed a long illness.

Few lawyers have faced greater challenges than confronted Mr. St. Clair as the president's attorney in 1974 with the drumbeat of Watergate revelations mounting, his client increasingly beleaguered, and ominous talk circulating of constitutional crisis.

On July 8, 1974, he appeared before the Supreme Court to contend that the president was shielded by executive privilege from the efforts of Watergate Special Prosecutor Leon Jaworski to obtain the notorious Watergate tapes. Ten days later, Mr. St. Clair made his final arguments before the House Judiciary Committee as it prepared articles of impeachment against Nixon in connection with the notorious 1972 break-in at Democratic National Committee headquarters.

One of the members of the committee, Caldwell Butler, was later quoted in "The Final Days," by Bob Woodward and Carl Bernstein, as crediting Mr. St. Clair for a "masterful presentation" that would have carried the day had the panel been a jury.

But the committee voted articles of impeachment, the Supreme Court ruled in the historic case of United States v. Nixon that the tapes would have to be surrendered, and Nixon resigned in August.

Years later, another member of the impeachment panel described Mr. St. Clair as his hero, one whom other lawyers might well emulate. Former representative Robert F. Drinan (D-Mass.), a Jesuit priest, wrote in the newspaper Legal Times in 1996 that Mr. St. Clair "did what lawyers are supposed to do -- tell your client to obey the law and maintain inviolate the confidences of your client."

Twenty-two years after Nixon resigned, Drinan wrote, "Mr. St. Clair continues to refuse to write, speak or even refer to his role as counsel" to the former president.

In their book, Woodward and Bernstein wrote that Mr. St. Clair, who had long been a lawyer with the firm of Hale and Dorr, was unmatched in trial preparation and "was reputed to be a courtroom wizard."

Before Watergate, he had been in Washington in the 1950s as an assistant to Joseph Welch in representing the U.S. Army before the Senate investigating panel led by Sen. Joseph R. McCarthy (R-Wis.)

Mr. St. Clair was born in Akron, Ohio, and graduated from the University of Illinois. He received a law degree from Harvard in 1947 after studies that were interrupted by Navy service in World War II.

During more than 40 years at Hale and Dorr, he dealt with many high-profile assignments, including some in which his time was donated. In one criminal defense case, bodyguards accompanied him to court. In a 1984 interview with the Boston Globe, he declined to disclose the advice he gave Nixon but said, "I approve of the fact that he did resign in the national interest."

Survivors include his wife, three children and eight grandchildren.