Sunday's Memorial Day concert (7 p.m. on Ch. 7) from the west lawn of the U.S. Capitol will offer lively music from the eras of World Wars I and II, Korea and Vietnam, played by the National Symphony Orchestra, and the more-haunting strains of the poignant theme from "Schindler's List," played by violinist Robert McDuffie.

But what you may remember most might well be a letter by a Massachusetts widow who lost her 19-year-old son in Vietnam 30 years ago. The mother, Theresa Davis, will be there to listen to actress Christine Lahti read it."It's such a powerful letter," remarked Lahti from a set in Toronto, where she was finishing a television movie. "I almost couldn't get through it, it's so powerful. What with the orchestra behind me, I hope I can get through it. I'm so honored to be part of this."

Lahti, who plays Dr. Katherine Austin on CBS' "Chicago Hope," is the daughter of a surgeon who served as a medic during World War II.

Davis, national president of American Gold Star Mothers, and seven other members of her group will be seated in the front row and VIP section at the concert. Pictures of their lost sons will be part of the film footage that accompanies the concert.

Davis' eldest child, Richard, a Special Forces Green Beret, was killed June 6, 1968. In the letter that Lahti will read, written for this occasion, Davis recalls also having received the folded American flag for the death of her husband, an Army master sergeant who was killed in an accident at White Sands, N.M., missile range.

Davis has attended most National Memorial Day concerts, coming to Washington each Veterans Day, Memorial Day and on Gold Star Mothers Day, the last Sunday in September. As 1997-98 president of the group, she stays at the organization's headquarters and makes certain to visit the Vietnam Veterans Memorial and Tomb of the Unknowns.

On the day Defense Secretary William S. Cohen ordered the exhumation and identification of the remains of the Vietnam veteran buried there, Davis considered his action, which was requested by the family of Air Force 1st Lt. Michael Blassie, believing he may be the soldier in the crypt.

"I can see the family's point, but in a way it's almost like desecrating the Tomb of the Unknowns," Davis said. "I go there a lot, and I don't think I would do it. I would just feel that even if it was my son, or even if it wasn't, it's still somebody's son. If I even had the remotest thought that it was my son, I would be honored (to have his remains entombed there)."

Davis said her group, founded 70 years ago for mothers who have lost a child on active military duty, "is dwindling. We're down to 2,000 (members) nationwide. A lot of people don't join because they think all we do is sit and cry, but the main purpose is to keep the public aware that we did lose sons (or daughters) - a lot of people do lose sight of that."

In addition to Lahti, participants include World War II veteran Charles Durning, holder of a Silver Star and three Purple Hearts, who will recollect the day he helped liberate prisoners from a Nazi death camp; and actor Richard Dreyfuss, who will narrate documentary war footage and read John McCrae's World War I poem "In Flanders Fields."

Singers Pam Tillis, Leslie Uggams, Jack Jones and Gary Morris will perform a selection of songs including "It's a Long Way to Tipperary" and more-recent selections such as "Tie a Yellow Ribbon" and the Vietnam-era "Aquarius."

The NSO, under the baton of Erich Kunzel, will play Beethoven's Fifth Symphony, Third and Fourth Movements, while the audience sees footage of defining moments of the Cold War, including the Berlin Airlift, Cuban Missile Crisis and fall of the Berlin Wall.

Actor Ossie Davis, a World War II medic, will host the concert.