Elliot L. Richardson was remembered yesterday in the nation's capital for six decades of public service and one searing moment of defiance as U.S. attorney general when President Richard M. Nixon tried to derail the Watergate investigation.

More than 1,000 people attended Richardson's memorial service at Washington National Cathedral, remembering the man who resigned Oct. 20, 1973, rather than follow Nixon's order to fire Archibald Cox, the special prosecutor investigating the break-in at Democratic Party headquarters in the Watergate Hotel.

Richardson, 79, died New Year's Eve in Boston of a cerebral hemorrhage.

Those who attended yesterday's memorial included his two sons and a daughter, with their families, Supreme Court Justice Sandra Day O'Connor, Attorney General Janet Reno and Sens. Edward M. Kennedy (D-Mass.) and Charles S. Robb (D-Va.).

Richardson held more Cabinet posts than any other American--four--and was Nixon's attorney general, secretary of defense and secretary of health, education and welfare and President Gerald R. Ford's secretary of commerce. Among his other government assignments, he served as ambassador to Britain and negotiated the worldwide treaty on the Law of the Sea. Early in his career, he was elected lieutenant governor and attorney general of Massachusetts.

"He provided a symbol of public virtue for a society on the edge of cynicism," said Richard Darman, Richardson's assistant at the Justice Department when he refused to dismiss Cox during what became known the "Saturday night massacre." "He helped turn a night when the FBI seized the office of the attorney general into a day when America's constitutional strength was reaffirmed."

Darman noted wryly that Richardson once looked at his dogs sleeping in the sun and wondered whether "they might prefer to be hitched to a plow. . . . He saw work as a service and the opportunity to serve as a precious gift."

Sir John Thompson, former British ambassador to the United Nations, remembered Richardson as a friend who "threw a calculated game of darts and was a good judge of malt whisky." He disliked being called a "blue-blood or Brahmin," Thompson said.

"He was, through and through, a man of government, a great public servant who put principle before pride or preferment," Thompson said.

Ernest J. Sargeant, a friend from their student days at Harvard College and Harvard Law School, said Richardson, who lived in Mitchellville, remained rooted in the family home in his native Eastham, Mass., where "one of Elliot's greatest pleasures" was to see his grandchildren swim and fish for flounder in the salt ponds where he had played as a boy.

Darman said Richardson's service extended from the D-day landing at Normandy--where he saved a fellow officer from a minefield and earned a Purple Heart and Bronze Star--to his embracing of causes and interests large and small.

He was as enthusiastic about bird-watching and fly-fishing as he was about youth programs and good government. "History is full of people deemed great in their public lives and found in private to have defects proportionate," he said. "Not so with Elliot." As a family member, "conservationist, educator, mediator, adviser and advocate of worthy causes," Darman said, Richardson "met the same extraordinary standards as in the public sphere."

Others at the memorial service included Russell Train, a founder of the World Wildlife Fund, and David Ives, past chairman of the National Association of Public Television Stations.

The nonprofit Council for Excellence in Government has established a prize in Richardson's name to honor excellence, integrity and creativity in government service.

CAPTION: More than 1,000 people attended the memorial service for Elliot L. Richardson at Washington National Cathedral. He was remembered as "a symbol of public virtue for a society on the edge of cynicism."