Thousands of former Peace Corps volunteers marched yesterday, in a line that stretched from the Lincoln Memorial across the Memorial Bridge and into Arlington National Cemetery, on a day of memory for 199 colleagues who died in service and a day of renewal for Peace Corps ideals that did not.

The bright-colored flags of dozens of nations fluttered in the sultry breezes as former volunteers and their families held them aloft and marched to the cemetery, first to lay a wreath at the grave of President Kennedy, who established the Peace Corps in 1961, and then to the amphitheater to honor those who died at their Peace Corps posts. The march and ceremony were part of a celebration of the corps' 25th anniversary.

"Until now, our grief had been a private matter," said Gordon Radley, whose brother Lawrence and volunteer David Crozier were the first Peace Corps members to die in service. "But as I stand today in our national cemetery, I realize . . . that they were a part of you as much as ours . . . . The ideals and values they embraced are the heart and soul of our nation."

Shortly after the speech by Radley, whose brother died in a 1962 plane crash in Colombia, relatives of other volunteers who died were handed single yellow roses by Peace Corps Director Loret Miller Ruppe and Sargent Shriver, the corps' first director. Most of the deaths occurred in accidents, though there have been 10 murders and a few suicides.

Clutching the rose in one hand after the service, Marge Kenney of Valinda, Calif., spoke of her daughter Ann, who died in 1971 in a boating accident while a teacher on the Pacific island chain of Micronesia. "Why did she go?" Kenney mused. "Why does anybody want to go? It was a spirit that caught on during the Kennedy years, and she was fired up at the time.

"People called them hippies in the '70s. But they woke us up to a lot of things . . . and we could use that spirit again."

Much of the day's talk, both on the podium and among the marchers, centered on the need today for that spirit of peace and giving. "We have in a sense come full circle," said Bill Moyers, a CBS commentator and former Peace Corps deputy director, who officiated at the service. "The Peace Corps was born after a long season during which young Americans had been spiritually unemployed . . . . Now, once again, a generation of Americans is tempted to live undisturbed, buying tranquility on credit while hearts atrophy, quarantined from any great enthusiasm but private ambition."

But many of the alumni and former and current officials, Moyers among them, said they think that some Americans still believe in the values that sent a previous generation into the far reaches of other continents.

Ruppe is fond of saying that she can "still see the same stars that Sargent Shriver saw in the eyes of young people in America. It just hasn't been utilized."

In a quarter century, more than 100,000 volunteers have served in 92 nations. Though some administration officials have recommended disbanding the agency, the Peace Corps has a current annual budget of $ 128 million and 6,000 volunteers in 62 countries, and it gets about 5,000 calls each week for information.

"Some of us get cynical and think there are no idealists out there, but there are," said Peter Johnson, a Peace Corps alumnus who served in India in the late 1960s and now recruits for the corps in California. "Volunteers are more pragmatic now. They ask, 'How will this help me in the future, as a teacher, or in industry?' But they have to have a little idealism. They couldn't last for two years [in a foreign country] without it."

Yesterday, memories of the past and hope for the future were on a lot of minds. John A. Olsen III, who served with his wife in Micronesia from 1969 to 1971, wanted their 2-year-old daughter Margot to keep the silver balloon marked "Micronesia" that had been used to draw alumni to the proper spot in the marching line.

"One day my children may understand the honor we had," said Olsen. "One day my children may get that opportunity themselves."