Two of Washington's major musical institutions will have important anniversaries this season: the 50th for the free Sunday evening concerts in the National Gallery of Art and the 25th for the Washington Performing Arts Society. Both organizations will celebrate the anniversaries throughout the season, primarily by doing what they do best -- bringing some of the world's most interesting musicians to perform in Washington.

The National Gallery, which has its own orchestra and vocal ensemble, also will produce a number of special programs, including a world premiere (Daniel Pinkham's Symphony No. 4) on Nov. 4. There will be an unusual number of performers with high name recognition in the season's gallery concerts, which usually focus on fine but relatively unknown performers. The list includes soprano Martina Arroyo, pianist Shura Cherkassky, violist Emanuel Vardi, violinists Daniel Heifetz and Oscar Shumsky, and pianist Anton Kuerti.

WPAS has been bringing the world's leading ensembles and soloists to Washington since it was founded by Patrick Hayes a quarter-century ago, and its upcoming season will be busier than ever. Besides such noted soloists as Jessye Norman, James Galway, Alfred Brendel and Mitsuko Uchida and such hyper-popular groups as the King's Singers and the Canadian Brass, it will bring a mind-boggling list of orchestras to play at the Kennedy Center. That list includes (in chronological order): the Philadelphia Orchestra in September and November; the Royal Concertgebouw Orchestra of Amsterdam; the BBC Concert Orchestra, Royal Air Force Marching Band and the BBC Chorus, performing what promises to be a memorable concert marking another anniversary, the 50th of the Battle of Britain; the Czech Philharmonic, the Boston Symphony, the Japan Philharmonic, the Lenigrad Philharmonic, the Salzburg Mozarteum Orchestra, the Vienna Philharmonic, the Cleveland Orchestra, the Houston Symphony, the Israel Philharmonic, L'Orchestre National de Lyon, the English Chamber Orchestra and the Vienna Chamber Orchestra.

University Community Concerts, celebrating its 15th anniversary, will give most of its concerts, as usual, on the University of Maryland campus, but two vocal ensembles specializing in early music will be sponsored at acoustically appropriate locations in Washington: Sequentia at the National Presbyterian Church in October and the Taverner Choir and Consort at the Washington Cathedral in February. Also at the cathedral, the Gay Men's Chorus of Washington will open its 10th-anniversary season in October with an interdenominational AIDS healing service.

The Center for the Arts at George Mason University will not celebrate its 10th anniversary for another 10 years, but by then it may well have changed the face of performing arts in Northern Virginia. Besides housing the university's own busy performing arts activity and providing a new home for the Fairfax Symphony Orchestra, it will present a series of world-class performers in a new auditorium comparable in size and quality (and superior in parking facilities) to any hall in the Kennedy Center.

Notable attractions in the upcoming season will include the Pittsburgh Symphony with Lorin Maazel conducting, the Boy Choir of Harlem, Leontyne Price, Mozart's "The Marriage of Figaro" performed by the New York City Opera National Company, Itzhak Perlman, the Academy of St. Martin-in-the-Fields, I Solisti Veneti, Yo-Yo Ma and the Canadian Brass -- programming calculated to fill any concert hall in the world.

Nationally, the most important musical anniversaries of the year will include the 100th of Carnegie Hall, the 90th birthday of Aaron Copland in November and the 80th birthday of William Schuman, which happened in August but will be celebrated by American orchestras all year. David Diamond, who celebrates his 75th birthday this season, will be featured in the American Composers series in the Terrace Theater, as will Pulitzer Prize winner Mel Powell.

The opera season will become very crowded on the first weekend in November, with three opera performances in a little over 24 hours. First, the Prince George's Opera will perform "La Traviata" in what is rumored to be a striking new interpretation at 8 p.m., Friday, Nov. 2, at Prince George's Community College. At 2 p.m. the next day, it will be Handel's "Agrippina" as part of the University of Maryland Handel Festival. Then, at 7 p.m., the Washington Opera will open, with "Salome," a season that will undoubtedly be sold out long before the first curtain goes up. Other attractions offered by the Washington Opera this season include "La Boheme," "The Magic Flute," "Purcell's "King Arthur," Menotti's "The Saint of Bleecker Street," Massenet's "Manon" and "Rigoletto."

The Prince George's "Traviata" will have a repeat performance, Nov. 4 at Lisner Auditorium. The opening of this downtown venue may be a major breakthrough for the always interesting Prince George's company.

Less familiar operas coming this fall will include Donizetti's "Lucrezia Borgia," performed later this month at Lisner by the Washington Concert Opera; "The Jumping Frog of Calaveras Country," based on the Mark Twain story, presented by the Opera Theatre of Northern Virginia in December, and a Halloween performance of a vampire opera, "La Contessa dei Vampiri," by the Handel Festival Orchestra (which will also have a busy season of subscription concerts and will continue its highly successful series of children's concerts).

"La Contessa dei Vampiri" may provoke more interesting conversations than any other vocal event of the fall season -- with one exception. That, predictably, will be the Washington debut of baritone Gordon Getty (previously known here only as a composer) singing Schubert's "Die Schoene Muellerin" at Gaston Hall in the Schubert, Schubert and Schubert Festival in the last week of October. Tickets (still only $5) are likely to be scarce.

The most remarkable guest appearance with the National Symphony Orchestra during the fall season will be the Beaux Arts Trio later this month, performing (what else?) Beethoven's Triple Concerto. Music Director Mstislav Rostropovich will conduct all the subscription concerts in September and the first two weeks of October, including the world premiere of Vyacheslav Artyomov's Symphony Sept. 20. Guest conductors will include Zdenek Macal, Alessandro Siciliani and John Eliot Gardiner. Featured soloists will include violinists Joshua Bell and William Steck, flutists James Galway and Toshiko Kohno, cellist Wendy Warner, pianists Justus Frantz and Tzimon Barto, and organist William Neil.

One of the major events in American music each year is the Kennedy Center Friedheim Awards: a free concert of distinguished American music composed within the past two years, followed by the presentation of $9,000 in prizes to those found best by a panel of judges. This year's Friedheim Awards will be held Oct. 28 in the Kennedy Center Concert Hall. The finalists, orchestral compositions by Frederick Bianchi, Daron Hagen, William Kraft and Ralph Shapey will be played by the Orchestra of the Mannes College of Music, Michael Charry conducting.

This season's Terrace Theater concerts, booked by Marta Istomin before her resignation earlier this year, reflect as usual her perceptive musical taste tempered by awareness that no profits can be made in that acoustically outstanding but very small auditorium. As usual, many of the performers will be unfamiliar -- the Terrace concerts have become a traditional place for discovering fresh talent -- but there also will be some well-known musicians, including the Guarneri String Quartet, violinist Daniel Heifetz doing Vivaldi's "The Four Seasons," and pianists Richard Goode and Lee Luvisi. Others who should be well worth hearing include cellist Takeichiro Hirai, the Shanghai String Quartet, the Cleveland Institute of Music Chamber Players and the West German Sinfonia.