HOWARD HANSON was the dean of American composers when he died on Feb. 26, at the age of 84; his passing was little noted, probably because we simply don't hear much of his music nowadays, and his contributions to American music beyond his own compositions went unmentioned.

Actually, Washington has probably heard more of Hanson's music than most other communities outside of Rochester, N.,Y., where Hanson rolled up a remarkable 40-year tenure as director of the University of Rochester's Eastman School of Music (1924-64). Hans Kindler conducted the National Symphony Orchestra in Hanson's Second Symphony (the "Romantic," by all odds his most popular work) in March 1944 and nine years later Hanson himself conducted the NSO in his Fourth (the "Requiem," in honor of his father, which won him a Pulitzer Prize in 1944) and the suite from his opera "Merry Mount."

Richard Bales, a distinguished Eastman alumnus, has presented Hanson's works with some frequency in his National Gallery concerts, acquainting us with the big, sweeping Third Symphony and the shorter but big-boned First ("Nordic"). These and the tightknit Sixth written for the New York Philharmonic in 1967 would be welcome in any orchestra's programs.

But if Hanson's own music never succeeds in establishing itself in the permanent repertory, the man must be remembered with honor for his extraordinary service as a champion of the cause of American music. He is still in his 30s when he made the Eastman School a citadel of that cause. True, his conservative tastes kept him from going very far in the direction of experimental music or any sort of avantgardisme , but the annual Festival of American Music that he created, planned and personally conducted drew the faithful to Rochester to be introduced to new works by such composers as Copland, Barber, Riegger, Carter, Sessions, Piston, Thomson and Mennin, and for revivals of music from our all but forgotten past.

The attractive little Sowerby overture, "Comes Autumn Time," that Rostropovich and the NSO performed here in mid-February, was familiar to most of us who knew it at all only through a 78-rpm disc Hanson and the Eastman-Rochester Orchestra recorded for Victor more than 40 years ago. At the same time he recorded music by John Knowles Paine, William Grant Still, MacDowell, Griffes, Chadwick -- and his own "Romantic" Symphony.

The recording program thus begun was eventually to take American music to millions who could never have made the pilgrimage to Rochester. After World War II there were two or three LPs for Columbia, and then the unforgettable series for Mercury.

Many of these valuable recordings have been reissued in Mercury's Golden Import series, and several others have been revived on the school's own reprint label, Eastman Recorded Archive. Among them are the first five of Hanson's symphonies -- all in more than respectable sound except the monophonic Fourth, which came out sounding wiry in the Dutch remastering -- and perhaps 50 other unavailable works by almost as many American composers, both well-known and lesser-known. Among the more interesting items in this category (titles unavailable elsewhere) are these discs, available now in the Golden Imports series:

Barber: Capricorn Concerto; Sessions: "The Black Maskers"; Ginastera: Overture to the Creole "Faust" SRI 75049.

Carpenter: "Adventures in a Perambulator"; Moore: "The Pageant of P.T. Barnum"; Nelson: "Savannah River Holiday" SRI 75095.

Carter: "The Minotaur"; Cowell: Symphony No. 4; Riegger: New Dances SRI 75111.

Chadwick: Symphonic Sketches; Piston: "The Incredible Flutist" SRI 75050.

Hanson: Symphonies Nos. 1 and 3 SRI 75112.

Mennin: Symphony No. 5; Griffes: Poem for Flute and Strings; Schuman: New England Triptych SRI 75020.

Piston: Symphony No. 3; Hanson: Symphony No. 4 SRI 75107.

Thomson: Symphony on a Hymm Tune; "The Feast of Love"; Hanson: Four Psalms SRI 75063.

To this short list must be added the important recording of Wallingford Riegger's Third Symphony, now on CRI 284, and the only recording of the Hanson Sixth, performed not by the composer in this case but by the Music for Westchester Orchestra under Siegfried Landau, on Turnabout TV-S 34534. The material on ERA is generally of somewhat lesser interest, but it is worth perusing, as are the other Golden Import reissues.