The program of American string quartets at the National Gallery of Art last night was dominated by two works from the romantic-impressionist mode of the '30s and '40s. That's the school that produced what is by far the most famous piece of American chamber music, the adagio from Samuel Barber's Quartet, better known in its orchestral garb as the Adagio for Strings.

Last night's works, which were played as part of the gallery's 39th American Music Festival, weren't of such individuality or sustained intensity as the Barber, but in places they did not suffer greatly by comparison.

One adagio, the slow movement of Robert Palmer's Quartet No. 2 ("In Memory of Natalie Koussevitsky") was especially distinguished; the work was an early one commissioned in 1943 by Serge Koussevitsky and recently revised. It begins with a melancholy, long-lined song in the low strings that keeps returning in different forms and finally disperses. Unlike most of what was heard last night, this movement is more than just listenable, well-crafted music. It grabs and holds you. Throughout, the Palmer had a stronger pulse than the other works.

The Quincy Porter Quartet sounded as though it was derived from the quartets of Debussy and Ravel. The principal subject was usually in the first violin; the other instruments gave support that was more atmospheric than aggressive.

Opening the program was a recent quartet by James Willey that was neither entirely tonal nor entirely atonal, though it was more the former. Willey was particularly preoccupied with sonorities in this six-section work of one movement; the sections shared a common progression of notes. The composition was tight and fleet.

The Tremont String Quartet was assured and idiomatic. But matters of balance and texture are hard to judge in so reverberant a room as the East Garden Court.