More than any single event in a year that had more disappointments than triumphs, 1976 suggested we now have two American theaters, New York's and the rest of the country's.

This is not necessarily a bad thing. Each theater community should be unique to itself. We have our Arena Stage and Folger. San Francisco, Los Angeles and Seattle are developing in their own ways. New York's theater gets - and deserves - the most attention.

Still, one must pause about what New York misses in failing to appreciate "A Texas Trilogy" or "Pacific Overtures," one of the true creative efforts of our musical stage's Bicentennial year (and which went on to win the New York Critics Circle award as best musical).

The most recent instance is "Music Is," the George Abbott-Richard Adler musical from "Twelfth Night." No one in Seattle or Washington called this a great musical, but it had charm, professionalism and audience response strong enough to have Roger Stevens wishing he'd booked it for three months in the Eisenhower. It lasted only a week in New York.

By the beginning of the year, the Kennedy Center's Bicentennial series had proved erratic. January opened with "Rip Van Winkle." The audiences for Joseph Jefferson's historic 19th-century triumph disappeared.

March heard the bells toll for the big musical plays, now so expensive to produce with splash that they may become exinct. Though Richard Rodgers had written a fine score for "Rex" (listen to the disc), the lavish spectacle never did pull itself together, though it did improve somewhat during the Opera House tryout.

The best memory of "1600 Pennsylvania Avenue" is that it put the National back on the map for the fine theater it is. Because the Leonard Bernstein-Alan Jay Lerner musical about the White House was something people were curious about, the National got rolling again.But the million-plus dollars lost had a sobering effect of future musical producers and their angels. Again, the concept had no been clearly developed, and remained only a general idea.

April had some cheer, especially the first Tony recognizing a non-commercial New York theatrical company. Arena Stage, so strong a national influence, was the first recipient of what will be annual recognition for theaters across the land. And Arena's activities since have more than justified the honor. It began its season with three productions on three stages in as many weeks - all of high quality.

A Tony - and later a Pulitzer - went to "A Chorus Line." The musical by Michael Bennett, James Kirkwood, Nicholas Danate, Marvin Hamlisch and Edward Kleban had been a collaborative effort by those men and, as well, by the dancers of the original company. This is a novel way of doing things in the theater and its enormous success is wipping out the debts of Joseph Papp's New York Shakespeare Festival. April also brough the eighth annual American College Theater Festival.

May brought the three Texas plays of Preston Jones into the Kennedy Center for a stay that totalled over 17 weeks. The adulation proved dangerous.

Spring and summer stressed how elusive quality can be. The French gift of Sound and Light to Mount Vernon was most welcome but was tied to a script which did little justice to the subject, indeed could have the effect of deferring further the illuminating device for other national shrines. Quality in concept, writing, music and imagination, on the other hand, were visible in "The American Experience" on 13th Street, a Bicentennial creation which deserves to become a permanent fixture.

Black theater, while riding high in the popular musicals - "Bubbling Brown Sugar," "Guys and Dolls," "The Wiz" and "For Colored Girls" - had two Washington failures, but other quiet successes. The D.C. Black Rep, ehich never was a repertory company, and never did manage to create anything its audiences cared to support, gave up in the Fall. Paul Allen's efforts to vitalize L'Enfant Plaza's hard-to-find American Theater also failed. But Howard University's drama department remains a leader of black theater. The Federal City College Poor Man's Theater is an exciting place. O Street saw information of the loftily named Paul Robeson Multi-Media Center. Accenting ethnic theater, Black Alley now lives in the inner city as well as uptown.

There was no black drama in the kennedy Center's Bicentennial parade, but not for lack of trying to find one. The center's roof terrace exhibit, "America on Stage," gradually caught on as a worthwhile place to visit. Through her knowledgable artistry, Eugenia Rawls showed that its Chautauqua Tent could be well used and she drew crowds for her extended run in three mono-dramas about vivd American women.

A summer visit from Zero Mostel's "Fiddler on the Roof" a revival of a fine musical presented with expensive integrity, proved that this American form has vast appeal While Pearl Bailey's "Hello, Dolly!" had been an outrageously tacky production, Mostel's "Fiddler" was superb in all details. Christmas brought it to New York, where it once ran for 3,242 performances.

Outdoor theater accented our 200th birthday. Into its third summer, the staging for St. Mary's City "Wings of the Morning" showed how dogged patience can improve matters. The Paul Green "We the People," at Merriweather Post Pavilion, revealed how impatience can be disastrous. It had the air of something pieced together by too few in too short a time with too little money. Contrary to some expectations, the Marriott's young singers and dancers at the Sylvan Theater revealed a crisp, professional and free entertainment which delighted thousands.

The Smithsonian's two-month folk festival was another free outdoor treat. And the impeccable artistry of Julie Harris as Emily Dickinson in "The Belle of Amherst" showed how vital a long nuturing process can be.

Their craft refined by eyars of experience, John Gielgud and Ralph Richardson immersed us in a purposeful bafflement David Storey titled "No Man's Land." David Merrick seemed to have lost his producing touch with "The Baker's Wife." Eva Le Gallienne and an excellent company returned "The Royal Family," but for a play that sold out last year, it met baffling indifference. Tom Stoppard's little British farce, "Dirty Linen" seemed just right for the West End, out of place when it moved to the Eisenhower.

Not a rich country, Ireland made a final contribution for the Bicentennial, the Abbey Theater of Dublin in O'Casey's "The Plough and the Stars," a very great play. The Folger has been decisively adding to the city's amenities with exhibits, music, poetry and publications, especially Charles Shatuck's "Shapespeare on the American Stage" and the Folger Theater Group. Its seventh season finds this adventurous company constantly improved.

If a summation of 1976 is twinged with disappointments, such is the nature of great expectations.