The Library of Congress will open its 53rd season this week on Friday night when Frederick Fennell will lead a wind ensemble in music by Florent Schmitt, Gounod, Richard Strauss, and the Gran Partita, K. 361, by Mozart. MAJOR CHANGE: Library programs will begin at 8 p.m., a half-hour earlier than usual. And a fine idea, too. Note, 8 p.m.

The weeks immediately ahead will bring the Juilliard Quartet back to the Library on the first three Thursdays and Fridays in October, with Rudolf Firkusny joining them on Oct. 6-7. The King's Singers will sing in a special sunday afternoon concert on Oct. 30.

The National Symphony Orchestra opens its 47th season next Tuesday night with its fourth music director, Mstislav Rostropovich, in charge of things, and Rudolf Serkin as guest soloist. Serkin will play the Beethoven Fourth Concerto; the overture will be Weber's "Oberon," and the symphony the Dvorak No. 7. The program will be heard on Tuesday, Wednesday, and Thursday nights. The following week will be all-Bernstein, with the composer here as composer-conductor, Rostorpovich as cellist-conductor, and the world premiere of Bernstein's "Songfest."

Virginia Intermount College is making major music news in Washington this week: Pianist Kenneth Huber will play the National Gallery concert at 7 p.m., Sunday, and organist Stephen Hamilton will play at Washington Cathedral on Oct. 9. Both men are on the faculty of the college in Bristol, Va.

The Division of Music Instruments at the Smithsonian opens its season on Saturday night when Jan de Gaetani and Leslie Guinn give a joint recital. Some Washingtonians will remember when Guinn was baritone soloist at the National Presbyterian Church. Some may even remember when I was. Soprano de Gaetani and her partner will sign duets by Cornelius, Brahms and Schumann, with sings by Schubert and Mozart. Pianist Gilbert Kalish will play the Steinway that once belonged to Paderewski.

Maryland University is presenting Vera Schwartz in music for fortepiano and harpsichord, both solo and ensemble, on Saturday, at 8:15 p.m. in the Adult Education Center. Tickets at the door.

Children's Opera Theater, whose director is Michael Kaye, was recently awarded 10 CETA positions to continue its programs in Arlington County.

This means that CETA (Comprehensive Employment and Training Act) funding will create work for Arlington County performing artists and arts workers who will join in the Children's Opera Theater activities. If the same kind of action could be taken in Montgomery and Fairfax counties and the District of Columbia, the work done by this group in carrying opera to children, would be far more effectively spread out. For details, call Children's Opera Theater, 234-8617.

The Music Critics Association has new officers: Patrick Smith, president; Robert Commanday, of The San Francisco Chronicle, vice president; Michael Walsh of The Rochester Democrat and Chronicle, recording secretary; and John Rockwell of The New York Times, treasurer.

The Koussevitzky Foundation in the Library of Congress has awarded commissions to composers Sandor Balassa of Hungary, Donald Harris of Hartford, Conn., and Robert Lewis of Baltimore.