Evelyn Cressman stood on a grassy field near the Pentagon yesterday, one of 1,500 at a ceremony to commemorate National POW/MIA Recognition Day, as the national anthem played and four Air Force firghter-bombers flew overhead.

One of the planes peeled out of formation and flew straight up to the heavens, a symbolic "missing man salute." It reminded Evelyn Cressman of her son, Peter, whose plane was shot down over Laos a week after the Paris Peace Treaty was signed in 1973. She doesn't know if he is alive or dead.

"It's a constant state of limbo," said Cressman, the Florida chairman of the National League of Families of POWs and MIAs in Southeast Asia. "If they could tell us he was dead, we could accept that. But it's not knowing that's unbearable."

There are almost 2,500 Peters out there, men who went to war half a world away and have never been accounted for. Once it was fashionable to wear bracelets engraved with the name of a missing soldier. But things have changed, and these days mostly their familis carry their memories. Yesterday was meant to remind Americans once again.

Delivering a message from President Reagan, Secretary of Defense Caspar W. Weinberger said, "It is imperative on this day that we pay homage both to the men who have so profoundly demonstrated their devotion to America and the families of those courageous Americans who have borne such a great burden during the absence of their loved ones."

In his message, Reagan said he was "determined to obtain the fullest possible accounting" of those servicemen still missing.

Weinberger said the United States "will not stop pressing the governments of Indochina" on this issue. He dismissed as a "gesture" Vietnam's recent return in May of the remains of three U.S. military men whose identities have not yet been made public.

"We're going to keep the faith, we're not going to give up until we know something for sure," said George Schultz, one of the 140 relatives of MIAs or POWs who attended the ceremony. His son, Sheldon, an Army warrant officer and a helicopter pilot, was shot down over Laos in 1968. "It's nice to know that Reagan hasn't given up either."

The families who attended spoke of their limbo, how an empty seat at the dinner table is something they never quite got used to. Cressman said that since her son's disapperance, she stopped trimming the Christmas tree and making Easter eggs.

"I used to make eggs and put everyone's name on one," she said. "I felt funny putting Peter's name on one, and I felt funny not putting his nane on one. So I just stopped altogether."

Joe Cornell, 15, was six months old when his uncle, Air Force Col. Vincent Chiarello, was shot down over North Vietnam. Joe came with his family from Bucks County, Pa., for the ceremony, he said -- To honor him for fighting for what he believed in."

Would he fight for this country? "Sure, because I think that even though we did make a mistake in Vietnam, we learned something," Joe said. "I dont't think we'll make it again."