A REVOLUTION is coming to town this week, and it will be with us for quite a while. It begins, appropriately, with an enormous display of explosives -- fireworks on the Mall Tuesday night. But it will be nonviolent -- it is a cultural, not a political, revolution -- and it will focus on centers of cultural rather than political power, places like the Kennedy Center, the Library of Congress, the Corcoran Gallery, the National Academy of Sciences and university campuses. It is a quiet revolution, though insistent -- so quiet that its opening shots will be fired by a girls' choir in a church -- the Tapiola Choir of Finland in the National Cathedral -- Tuesday night while the fireworks are lighting up the sky over the Mall.

What we will be seeing and hearing all through the season in the "Scandinavia Today" festival is actually a small part of a much larger phenomenon that has been happening for about a century in music: the decentralization of Western culture. The festival deals with only a small part of this massive movement, developments in five small countries: Denmark, Finland, Iceland, Norway and Sweden. But these countries deserve a festival of their own not only because of the music's quality, but because it is so far from our usual focus of attention.

"Iceland is astounding," according to Washington pianist Alan Mandel, who has visited the Scandinavian countries twice in the past year, as a performer and a musical scholar. "It is a country of 200,000 people and five times as many cows, and I was amazed at the quality of the music there. In all the Scandinavian countries, there is a strong, vibrant movement for contemporary music. The powers that be see fit to put their money into performances of contemporary music rather than nuclear weapons, so that when a composer writes an opera it is performed. I am told on good authority that an opera by Per Norgaard of Norway got 160 rehearsals before its first performance. Many of the composers I talked to were in the middle of composing operas."

Mandel, who brought back "almost enough music to open a Scandinavian music center," is planning a Scandinavian festival in mid-January at American University, where he is a faculty member. Meanwhile, his conversation bubbles over with the names of unfamiliar composers: "In Sweden, Anders Eliasson is in the avant-garde -- extremely brilliant, complex and wild in his music . . . One of my personal favorites in Finland is Erik Bergman, 70 years old. I had a delightful visit, and we found we could communicate in German. His wife is a poet and he is very interested in percussion; his house is full of exotic African instruments . . . The whole myth that Scandinavians are cold people is a lot of baloney. I found them extremely warm and hospitable everywhere, even before they heard that I was planning a Scandinavian music festival."

Recognition of Scandinavian musical excellence has advanced very slowly in America and Southern Europe because our musical culture is essentially conservative and most Scandinavian music (like most American music) is modern. Music to be heard during the "Scandinavia Today" festival will range from an overture by the almost unknown Swedish baroque composer Johan Helmich Roman (performed by the Royal Swedish Chamber Orchestra under the auspices of the Washington Performing Arts Society) to the world premieres of pieces so new that their names have not yet been announced. There will also be some fairly familiar music by Grieg and Nielsen and the ever-popular Sibelius Violin Concerto, which is one of the world's half-dozen greatest. But the focus will be on music that has never before been heard in Washington and seldom heard outside Scandinavia.

The reason is that it takes considerable effort for a performer to master a new work, as it does for an audience to become accustomed to it. Who wants to spend time learning a difficult piece by someone named Thorkell Sigurbjornsson or Einojuhani Rautvaara when Brahms is easier and people will buy more tickets and applaud more enthusiastically? Most performers tend to continue along the lines that were set down for them in the conservatories, and these institutions live up to their name, conserving not only standards of performance but a set of attitudes and a particular kind of repertoire. Still, the revolution has advanced. Scandinavians began building their own conservatories in the last century -- Stockholm in 1864, Copenhagen in 1867, Oslo in 1894 -- about the time that audiences elsewhere began to become aware, in a slow and fragmentary way, of composers who were not German, French or Italian.

The first significant figure in this decentralization was probably Antonin Dvorak, a Czech who brought striking new melodic and rhythmic ideas into European music from his ethnic background. His prestige made it easier for other Czech composers -- Smetana, Janacek and Martinu -- and ushered in an era when musical idioms became more polyglot.

Washington will begin to experience what has been happening in Scandinavia with three concerts this week: the Tapiola Choir Tuesday night at the Cathedral; a concert by the New World Players, Stephen Kleiman conducting, Wednesday night at the National Academy of Sciences; and a concert by the Nordic Trio Friday night at the Library of Congress. The week will be studded with Washington premieres, as will the Oct. 10 program at the Corcoran by the Contemporary Music Forum, which has undoubtedly performed more new Scandinavian music already than any other ensemble in Washington.

The festival will return to the Library of Congress on Nov. 5 with a program by the Fresk String Quartet including the Quartet No. 5 ("Serenade") of Wilhelm Stenhammar, a neglected Swedish composer of the turn of the century.

The National Symphony will make its contribution to the festival at the end of November with two concerts of Scandinavian music conducted by Hugh Wolff and Mstislav Rostropovich in its regular subscription series. The programs will include a few older works (Grieg's Overture "In Autumn," Nielsen's Third Symphony and the Sibelius Violin Concerto), along with no fewer than five world premieres -- one of them a cello concerto by Arne Nordheim with Rostropovich as soloist.

Other major fall events include:

"Northern Light: Realism and Symbolism in Scandinavian Painting, 1880-1910," Friday, the Corcoran Gallery of Art (638-3211).

"William H. Johnson: The Scandinavian Years," Sept. 17, National Museum of American Art (357-2496).

The Tutak Theatre, Sept. 29-Oct. 5, Museum of Natural History (381-5954).

Scandinavian Poets Today, Oct. 12, Library of Congress Coolidge Auditorium (287-5000).

"Contemporaries: New Art From Finland," Nov. 19, Meridian House International (667-6800).