Wearing the medals of four wars, three generations of veterans gathered before the Tomb of the Unknown Soldier in Arlington National Cemetery yesterday to hear Secretary of Defense Caspar Weinberger pledge that "never again will we ask young men and women to serve in a war we do not intend to win."

"To keep peace with freedom, we must be so strong both in military force and in national will and resolve that no aggressor will choose to strike us or our allies," Weinberger told a crowd of 3,000 flag-waving veterans who gathered under sunny skies on Veterans Day and the 60th anniversary of the dedication of the Tomb of the Unknown Soldier.

In downtown Washington, also at the 11th hour of the 11th day of the 11th month -- commemorating the moment of the Armistice that ended World War I -- there was a different kind of Veterans Day gathering.

The scars and shattered limbs didn't show beneath their brown choir robes as 54 Vietnam veterans stood in a courtyard off New York Avenue. Neither did their emotional wounds as they began to sing.

The Young Veterans Choir, the members of which all are currently under treatment for post-traumatic stress syndrome at the Veterans Administration hospital in Menlo Park, Calif., came to Washington carrying messages in song and poetry and in reminiscences of a war that they continue reliving and continue escaping.

Most of the nation's 2.7 million Vietnam veterans came home years ago to schools, jobs and families. But these 54 are among those who are still making that journey home. Their message yesterday was that they don't want to carry forever the badge of Vietnam, that they want finally to be considered just as veterans, American sons, brothers and fathers.

"Finally, this is my veterans parade," said Fernando Valdez, 32, a Mexican-born former Army helicopter crew chief from San Diego. "It has been a very long time coming."

On Oct. 3, 1970, Valdez's helicopter was shot down over the central highlands of Vietnam. The crash severed his right arm, shattered his legs and blinded his left eye. He came home with more than 20 combat decorations, but the decade that followed his homecoming was a downward spiral culminating in heroin addiction, federal and state bank robbery convictions, four years in prison and, finally, mental collapse, he said.

Only in the last year, through the group therapy he shares with other troubled young veterans, Valdez said he has turned a corner, kicked drugs and started rebuilding. "I am trying to become an asset rather than a liability or a casualty," he said.

The Young Veterans Choir visit was organized by various veterans groups and by Rep. Tom Lantos (D-Calif.) who represents the hospital's home district. The visit coincided with the opening of an exhibit at Octagon House at 1799 New York Ave. NW, of the designs submitted for the new Vietnam Veterans Memorial, planned for a site on the Mall near the Lincoln Memorial.

The choir sang songs of love and brotherhood, and several veterans recited original poetry about their experiences.

"I am learning how to be a loving father and a loving husband for the first time," said Larry Connolly, a 33-year-old former marine who specialized in flame throwers and rocket assaults. Connolly, who landed in the Menlo Park program only after being turned away from other VA facilities, said he hoped the country would be reminded on Veterans Day of the need for such programs.

Connolly, who carries shrapnel in his legs, said he had grown increasingly paranoid and violent in recent years, slowly stockpiling an arsenal at his Northern California home and eventually accumulating four automatic rifles, a machine gun, a mortar, 200 pounds of explosives and 20,000 rounds of M16 rifle ammunition.

A few months ago, he said, he tried to run down his wife with a truck and then tried to kill himself, he said. His gun misfired.

"I have still been fighting the war and I am finally letting it go," Connolly said. "I am trying to become a normal loving American male . . . . I want people to know that."

With the planned construction of the new Vietnam Veterans Memorial, the war and its veterans are moving more firmly into America's official memory. While Vietnam veterans were in a small minority at Arlington yesterday, several veterans leaders said their organizations are seeing a gradual influx of these younger ex-servicemen.

"They're coming out of the so-called Vietnam syndrome," said A. Leo Anderson, chief of Veterans Affairs for the District of Columbia. "They're settling down, getting married, going into debt. They're coming back to reality."

Most of the Vietnam veterans who turned up at Arlington wore civilian garb, avoiding the conscious statement of the veterans organizations. "There are a lot of us around," said Jim Imparato, a 30-year-old Vietnam veteran from Philadelphia who drove here for the ceremonies. "Maybe we just don't want people to know it."

Imparato came to Washington with Max Inglett, 30, who is now in a wheelchair because of spine injuries received in Cambodia. Inglett, a Californian, decided last month to trek across the country, gathering support for a legislative program to prevent future Vietnams.

"He's got a lot of guts," said an admiring Imparato who decided to join Inglett's cause when he saw his fellow veteran on TV. But Imparato said he had always wanted to attend the Arlington ceremonies. "Veterans are veterans," he said. "I don't care which war they were in."

Yesterday, silence -- marred only by airplanes passing above -- greeted Weinberger, standing in for President Reagan, as he walked up the marble steps with former representative Hamilton Fish (R-N.Y.),92, to lay a red-white-and-blue wreath at the marble Tomb of the Unknown Soldier.

It was Fish who sponsored the 1921 bill, the last signed by Woodrow Wilson, to bring home an unknown soldier from the battlefields of World War I. Thirty seven years later, two more soldiers -- their names "known but to God" -- were buried in the marble tomb, honoring the dead of World II and the Korean War.

Yesterday, Neil Keltner, national commander of the Legion of Honor, which hosted the Arlington ceremonies, said a fourth soldier should be buried at the crypt in Arlington, one honoring the dead and missing from America's most recent war.

At about the same time, the Young Veterans Choir was singing its final song, "Blowing in the Wind," with its final question:

How many deaths will it take till we know

That too many people have died?