The Williamstown Theatre Festival has generally let ambition, of the right kind, rule its days and nights. The summer theater tucked away in the northwest corner of Massachusetts has certainly had its share of frivolous fare - the recently staged ''Holiday'' and past productions like ''Room Service,'' for example.
But some of the most ambitious theater the United States has to offer, assayed by some of the larger talents in American acting and directing, has graced the company's stages in this picture-post-card college town.
Last season's sprawling ''Tennessee Williams: A Celebration'' attempted something akin to those patchwork maps of the earth taken by satellite - nothing less than a complete survey of the playwright's uneven but immeasurable oeuvre. Artistic director Nikos Psacharo-poulos and his company gathered the characters that have for at least a generation haunted the American theater, and much of our national thought, into a 61/2-hour construction of scenes and soliloquies. The work could be taken over two days or, for the more daring theatergoer, in two sessions on a single day.
However you took it, ''Tennessee Williams'' was a revelation, as powerful a statement on this poet of the outcasts as you are likely to see anywhere.
Two seasons ago a production called ''The Greeks'' did for Greek tragedians what ''Tennessee Williams'' did for that Southern phenomenon. Built in similarly monumental proportions (over six hours' performance length), it also called attention to the company's goal of doing the spectacular and nearly impossible thing.
And so it has been with Nikos Psacharopoulos and the Williamstown Theatre Festival. We have come to expect nothing less from them than a vast undertaking each new season. A dangerous situation, really, because it could obscure the real reason for Williamstown's special place among regional theaters: The fact that Psacharopoulos attracts and nurtures the best acting talent available. Blythe Danner, Marisa Berenson, Edward Herrmann, E. G. Marshall, Christopher Walken, Sigourney Weaver, and Dianne Wiest make up the current batch of WTF regulars.
This star-studded approach hasn't always meant the most pinpoint accuracy in casting. A star on the door could mean a shot at a role that might better have gone to a lesser name. But the mixed ingredients in Williamstown productions tend to outlive a single errant flavor.
For example, this season's recently closed production of Anton Chekhov's seldom-seen early work ''Ivanov'' featured Christopher Walken in the title role. Ivanov is a kind of amoeba, a basically good man of no definite character, a moral sponge, passively soaking up the evil around him. Walken got all of this in his artful, highly watchable performance, but something essential was amiss. His ennui reflected the angstm of a 20th-century urban failure, while the words were those of a washed-out 19th-century rural aristocrat. In this case Walken simply didn't seem to understand the century or the country.
Almost everything else about this supple, lively production did work, however. Director John Madden built a clockwork Chekhov, with all the wheels turning perfectly, sounding the hours of the fading Russian aristocracy. Underneath the stifling blanket of time, Madden's ''Ivanov'' wriggled with life - malevolent, cheerless, grasping.
With works like this, WTF hardly needs a theatrical extravaganza to prove its merit. But it seems that Psacharopoulos has one of sorts in the works.
In a departure from past practice, the company has decided this season to present contemporary work. It advertised for plays and read more than 400 submissions this past winter. As a result, Williamstown has invited two playwrights, David Ives and Susan Yankowitz, to be in residence this summer. At least five other playwrights will be in mini-residence during the season.
Susan Yankowitz, who has written bloody, violent plays coming out of the confrontational idiom of '60s theater, as well as two books, brought her play ''A Knife in the Heart'' to Williamstown. The work was selected for use at last season's Eugene O'Neill Conference, and it will be presented on WTF's main stage this month. From the looks of the script, the play could be that ambitious, dangerous undertaking one looks for each year at Williamstown. It has that kind of sweep and passion and structural challenge. It also contains a couple of scenes that are likely to offend some playgoers.
Less than an hour after finishing a complete rewrite of the play, Miss Yankowitz, in a bright yellow slicker and carrying enough plastic bags to rival a New York bag lady, adjourned to a nearby inn and explained that the play emerged from a personal experience. Her son was born during the period John Chapman killed John Lennon; John Hinckley Jr. tried to assassinate President Reagan; and the child-murders in Atlanta held the headlines. Susan Yankowitz took it all grimly in as she watched her son growing in his first year.
''A Knife in the Heart,'' a play about a mass murderer and the effects of his deeds on his family, was born out of a deeply personal worry of a mother for her child's future. The play breathes with an intensity that is absent from some of Miss Yankowitz's other work. (''Monk's Revenge,'' a freely adapted version of a Victor Hugo story, hardly breathes at all. ''Slaughterhouse Play,'' a piece that was produced by New York's renowned Joseph Papp, breathes fire, but not much real life.)
Miss Yankowitz writes complicated, time-fragmented plays, somewhat like the long works that have dominated WTF's past two seasons. This one is no exception. It may not be as long as ''Tennessee Williams,'' but ''A Knife in the Heart'' is easily as complex and challenging. What the play lacks in depth of characterization it makes up for in sweep and intensity, even if some of the writing smacks of TV.
Reading the work in photocopied form (while it was still being twisted in rehearsal and rewrite through what Miss Yankowitz calls ''a few quarrels with Nikos''), you get the feeling that Williamstown has bitten off another knotty challenge. ''A Knife'' is a monumental play with a throbbing center. An ambitious undertaking, to say the least.
But then, these are ambitious people.