THE MUSIC season comes as an avalanche of nightly events, not as a neat concentration of weekly special happenings. In relation to the other performing arts, the pace is like the baseball season's compared with that of football.

This year's music avalanche may be a shade lighter than last year's--reflecting the state of the economy when the season was being planned. But ticket sales are moving briskly--a reflection of the state of the economy as the tickets go on the market. As the indoor season closes next June, the outdoor season may be expected to take off in high gear with the opening of the new, thoroughly fireproofed Filene Center, now in an advanced stage of construction at Wolf Trap.

The quality of the upcoming season seems as impressive as its quantity. Consider these prospects:

* The opera season looks unusually rich and varied. In November the Washington Opera will open with a new production of Mozart's "Cosi fan tutte," in which conductor Daniel Barenboim will make his American operatic debut. The season will continue with "Rigoletto" and "La Belle He'le ne" in the Opera House and Handel, Rossini, Donizetti and Menotti in the Terrace Theater. Meanwhile, in New York, the Metropolitan Opera will open its 100th season with "Les Troyens" Sept. 26 and a marathon gala Oct. 22 featuring practically every international opera star in the world. In Washington, the Metropolitan Opera's centennial season will offer more variety and quality than any this city has ever seen. Stars booked for the Washington season include Renata Scotto, Marilyn Horne, Placido Domingo, Jon Vickers, Sherrill Milnes and James Levine. The repertoire will include all of the season's new productions in a well-balanced menu of Britten, Mozart, Handel, Verdi, Puccini, Wagner and Zandonai. The Vienna Volksoper will present "Die Fledermaus" and a variety of operettas.

* At the National Symphony, music director Mstislav Rostropovich will be present for most of the fall before taking all of 1984 as a sabbatical year. Rostropovich will explore a variety of repertoire with which he is not usually associated, as well as such specialties as Shostakovich and Rachmaninoff. In November a special program will mark the 50th birthday of Krzysztof Penderecki with the composer present. In October, the orchestra will tour the southwestern United States.

* There will be a particularly full array of piano recitals, even for a city that is traditionally rich in them. At the Kennedy Center, besides the usual visits by Maurizio Pollini and both Serkins, there will be Barenboim's first piano recital here since 1969, and Eugene Istomin's first recital in the Concert Hall. The prospects look promising as well for the free Sunday recitals at the museums, with the esteemed young French performer Jean-Yves Thibaudet among the players in the Phillips Collection series. There will be no concerts at the Phillips Collection, which will be closed all season for renovations, but the traditional series will continue in the John Wesley Powell Auditorium, around the corner from the museum.

* In chamber music, there are dozens of series, ranging from the full-priced Chamber Music Society of Lincoln Center at the Kennedy Center to the prestigious, still a-quarter-a-ticket concerts at the Library of Congress, including the annual Juilliard String Quartet events. Other quartets appearing frequently in Washington this season include the Cleveland, Tokyo and Emerson. Chamber music will be happening in museums, including the Corcoran Gallery, the National Gallery, the Hirshhorn and the Renwick. And in churches all over town--notably the Dumbarton Avenue Methodist Church in Georgetown, whose series this year will feature members of the National Symphony Orchestra. Another church--Westminster Presbyterian--is the scene of several noteworthy chamber opera productions by Opera Southwest each season.

* Activities will escalate at the newest downtown hall for chamber music and one of the best--the splendid and underappreciated Terrace Theater at the Kennedy Center. In addition to the existing series, the Center will start a new Fortas Chamber Music series, in honor of the late Supreme Court justice and patron of music Abe Fortas. The landmark American Composers programs will open with Elliott Carter and will include Laurie Anderson and Gunther Schuller. The Washington Performing Arts Society will pay increased attention to Washington artists at the Terrace in four concerts that are already almost sold out.

In the suburbs, where music has expanded rapidly in recent years, notable chamber music series are planned at the Wolf Trap Barns, the Jewish Community Center, the National Institutes of Health and the University of Maryland. A benefit for the Community Concerts Series, at the University of Maryland's Center of Adult Education, will be given next month by Isaac Stern.

New music and old music are flourishing in Washington. Besides the work of specialized ensembles such as the Twentieth Century Consort and the Contemporary Music Forum, the city has a number of ensembles, such as National Musical Arts and the Theater Chamber Players, that put a strong emphasis on modern music. There are two special showcases for contemporary American music: the American Composers Series in the Terrace Theater and the annual Kennedy Center/Friedheim Awards, which will focus on chamber music this year. Finalists in the Friedheim competition, Oct. 8, are Ned Rorem, Karel Husa, George Perle, Thomas Oboe Lee and Aurelio de la Vega.

We can expect at least 20,000 performances of Handel's "Messiah" as the year nears its end. There will be more variety of repertoire in the two Handel festivals that have become annual traditions in Washington--one at the Kennedy Center, scattered through the season and directed by Stephen Simon; the other at the University of Maryland, concentrated in a single weekend in November and directed by Paul Traver.

American orchestras visiting the Kennedy Center this season will include those of Philadelphia, New York, Boston, San Francisco, Los Angeles (the Philharmonic and the Chamber Orchestra), Atlanta, Pittsburgh and (for the first time in seven years) Chicago. Foreign orchestras will include the Vienna and Czech Philharmonics, the Orchestre Nationale de France, the Hague Philharmonic, the English Chamber Orchestra, the Vienna Chamber Orchestra, the Stuttgart Chamber Orchestra, the Bamberg Symphony and the Danish National Orchestra. September

The National Symphony Orchestra will open its subscription season this week with music director Mstislav Rostropovich conducting the Second Symphony of Sibelius, Carter's "Holiday" Overture and Wagner's "Wesendonck Lieder" with mezzo-soprano Glenda Maurice. Programs later in the month will include the Seventh Symphony ("Leningrad") of Shostakovich, Rachmaninoff's seldom heard Fourth Piano Concerto and a variety of works with virtuoso solos featuring members of the orchestra. In New York, the Metropolitan Opera will open its 100th season and the City Opera will finally begin the season that was blocked by a strike last June. The Juilliard Quartet, with a little help from its friends, will present the two Brahms String Sextets and the Mozart Quintet in C at the Library of Congress. One of Washington's unique musical events, the Johann Sebastian Bach International Competition, will celebrate its 25th anniversary with contestants playing either Book I or Book II of "The Well-Tempered Clavier." October

Violinists of the month are Nathan Milstein, at the Kennedy Center, and Isaac Stern, who will give a gala benefit performance for the Community Concerts Series at the University of Maryland. Other violinists include Gidon Kremer, who will perform with the English Chamber Orchestra (Charles Mackerras conducting); Ida Levin, who will give a recital at the Jewish Community Center, and two soloist-concertmasters: Norman Carol with the Philadelphia Orchestra and Jody Gatwood with the Handel Festival Orchestra.

Notable nonviolinists will include sopranos Judith Blegen and Kathleen Battle. Also pianist-conductor Philippe Entremont with the Vienna Chamber Orchestra, clarinetist Richard Stoltzmann, cellist Carter Brey and pianist Veronica Jochum, who will be accompanied by her father, conductor Eugen Jochum, and the Bamberg Symphony. Cecile Licad, one of the most highly praised pianists of the younger generation, will appear with the Atlanta Symphony. Shura Cherkassky, a highly praised pianist of the older generation, will perform here for the first time in years, and a new trio--violinist Young-Uck Kim, cellist Yo Yo Ma and pianist Emanuel Ax--will perform here for the first time. The National Symphony will tour the Southwest for the first two weeks of the month. After the tour, guest conductor Erich Leinsdorf will lead the NSO in Bruckner's Eighth Symphony.

This month will see the opening of the season for many Washington performing and presenting organizations, including the Washington Performing Arts Society, the Wolf Trap Barns, the Theater Chamber Players, the Twentieth Century Consort, the Folger Consort, the Smithsonian Chamber Orchestra, the Washington Bach Consort, the Fairfax Symphony Orchestra, Paul Hill's Washington Singers, the Hesperus baroque ensemble, the American Chamber Orchestra and the Contemporary Music Forum. Opera Southwest will open its season with Stravinsky's "L'Histoire du Soldat" and Robert Starer's "The Last Lover."

Other highlights of the month will include a tribute to Elliott Carter, opening the Kennedy Center's American Composers Series in the Terrace Theater, the Kennedy Center/Friedheim competition for American composers of chamber music, and a festival of American music presented by the Washington Music Ensemble. November

The Washington Opera will open its season with Daniel Barenboim conducting Mozart's "Cosi fan tutte." The coproduction with the Orchestre de Paris, which is designed by Jean Pierre Ponnelle, was performed to rave reviews in France a few months ago. Three other Washington Opera productions will also open: Verdi's "Rigoletto," Offenbach's "La Belle He'le ne," Handel's "Semele" and Donizetti's "L'Elisir d'Amore." And as a welcome side effect Barenboim will play his first piano concert here in 14 years.

Krzysztof Penderecki's 50th birthday will be observed by the National Symphony with the composer conducting the American premiere of his Cello Concerto. Mstislav Rostropovich, to whom the work is dedicated, will be the soloist and the program will also include Penderecki's "Stabat Mater" and the world premiere of his "Requiem." In other November programs the orchestra will be conducted by Rafael Fru hbeck de Burgos and Hugh Wolff.

The University of Maryland's Handel Festival will fill a busy weekend, climaxing with a performance of his seldom-heard "Deborah," the second oratorio he composed to an English text. Not a part of the festival but in its spirit will be a performance of "Judas Maccabeus" by the Cathedral Choral Society. Other choral highlights of the month will include a performance of Copland's "In the Beginning" by the Paul Hill Chorale, Bach's "St. John Passion" by the Los Angeles Chamber Orchestra and the Gaechinger Kantorei, and Haydn's "The Creation" by the Ludwigsburg Festival Orchestra and Chorus. Not exactly a festival but certainly a celebration will be the performance of all four Brahms symphonies in two programs by Carlo Maria Giulini and the Los Angeles Philharmonic.

Violinist Salvatore Accardo will perform in Washington twice in November, once with the NSO and once with the Chamber Music Society of Lincoln Center. Ruggiero Ricci will give one recital. Pianists will be abundant, including Andre'-Michel Schub, Byron Janis, Horacio Guttie'rez, Jeffrey Kahane, John Browning and Alicia de Larrocha.

Highlights of the month in the Terrace Theater will include a tribute to Morton Feldman in the American Composers Series and performances by guitarist David Perry and soprano Barbara Hendricks. The second concert in the Abe Fortas series will be an evening of chamber music for strings featuring violinist Jody Gatwood. December

Amid a profusion of "Messiahs," there will be a few notable events (including two operas) without chorus. The Washington Opera will present a Menotti double feature, "The Medium" and "The Telephone," directed by the composer, as well as Rossini's "Cenerentola," also directed by Menotti. Rudolf Serkin will give a recital, as will Emanuel Ax, and the violin-piano team of Itzhak Perlman and Vladimir Ashkenazy. The rarely heard piano trio version of Schoenberg's "Verkla rte Nacht" will be performed by the Twentieth Century Consort and cellist Nathaniel Rosen will give a recital at the Jewish Community Center.