It was the evening of David Hibbard's last day as a Peace Corps volunteer in a mud-hut village in Nigeria when his overseas radio crackled with the bulletin that John F. Kennedy had been assassinated, and Hibbard's lonely nightmare began.

"I felt an overwhelming sense of loss and grief," said Hibbard, now a doctor in Boulder, Colo. "I stayed up all night listening for details. I wondered irrationally whether he might have lived if I'd stayed in Nigeria another year. I cried myself to sleep, exhausted."Jim Hagan of Santa Cruz, Calif., recalls he was a youngster trying to hitchhike out of a blizzard in Buffalo, N.Y., to attend the president's funeral in Washington. He never made it, but he joined the Peace Corps three years later for a stint in India.

Kennedy, said Hagan, embodied the Peace Corps' ideal of "helping others, breaking down barriers . . . and promoting peace instead of war."

Hibbard and Hagan were among 450 former Peace Corps volunteers or their surrogates who saluted Kennedy's memory during a 24-hour vigil in the Capitol Rotunda which ended at midday Tuesday, the 25th anniversary of the president's murder in Dallas.

They joined hundreds of other former volunteers at a memorial Mass at St. Matthew's Roman Catholic Cathedral, where the Rev. Theodore Hesburgh recalled Nov. 22, 1963, as the day when "the heartbeat of a nation stood still."

Americans across the land stood still for a moment Tuesday to recall that dark day, although members of the Kennedy family said they hoped the president could be remembered for his life, not his death.

"I think we should think of the high points of his life, the laughter and the vision," said Eunice Shriver, the president's sister, who made an early morning visit to his grave at Arlington National Cemetery. "Hopefully, someday we'll get excited about his birthday." Kennedy would have been 71 last May 29.

Robert Kennedy's widow, Ethel, appeared shortly after the cemetery gates opened at 8 a.m. Later in the day, Evelyn Lincoln, the president's personal secretary, laid three red roses before the eternal flame.

Thirty uniformed men of the Army's elite Green Berets laid a wreath, formed a semicircle and saluted their former commander in chief.

The president's youngest and only surviving brother, Sen. Edward M. Kennedy, D-Mass., laid a single white rose at the Kennedy memorial at Runnymede, England.