Given Rachmaninoff's penchant for expressing himself in large-scale proportions, a chamber music concert in which his work dominates is a fairly rare possibility. Last night at the Library of Congress, the second half of the program by the all-star Laredo-Delmoni-Rosen trio was Rachmaninoff, plus an encore.

Ruth Laredo is justly famed for her Rachmaninoff; she has recorded his complete solo piano works. She played four of the finest preludes, starting with the lyrical G Major and finishing with the stormy G-sharp Minor.

Then cellist Nathaniel Rosen joined her in the Rachmaninoff cello sonata, which became the passionate high point of a never less than excellent program. This work is unjustly neglected, partly because it comes out a little windy and too long in a routine playing. Last night proved that this in no way need be.

Rosen gave this work, one of the best cello sonatas, all the lyric rapture Rachmaninoff needs without once losing the structural logic. There was the alternation of nightmarish anxiety with melting lyricism in the scherzo, and the slow movement was all passion and love. The audience was so enchanted that Rosen and Laredo rewarded it with a cello transcription of the famous Vocalise.

Earlier came another neglected work, Koda'ly's youthful duo for violin and cello, with Rosen joined by Arturo Delmoni. The rhapsodic opening sounds very romantic and very Hungarian, with great rich textures. But the central movement introduces harmonic accidentals and percussive textural details that sometimes resembled Koda'ly's compatriot, Barto'k. Delmoni's violin playing was lovely but was overshadowed by Rosen at the cello--a very difficult part in which he was spectacular.