It's fascinating to watch, but 'Secret Honor' is no legitimate historic study of Nixon

Expletives undeleted, the 37th President of the United States has come to the Provincetown Playhouse here. He's the main character - the only character, in fact - of ''Secret Honor: The Last Testament of Richard M. Nixon,'' a blustery one-man show produced by the Los Angeles Actors' Theatre and presented Off Broadway by Robert Altman and Sandcastle 5 productions.

It's easy to take cheap shots at Nixon, just as James Whitmore took cheap shots at Harry Truman in his one-man show a few years ago. To its credit, ''Secret Honor'' tries to go beyond name-calling and scapegoating. The playwrights have credentials for this: Donald Freed is a historian and author; Arnold M. Stone is an attorney with government and private experience. And the star, Philip Baker Hall - who bears a passing resemblance to Nixon - balances the childishness of many passages with a performance that seems thoughtful as well as frantically energetic.

Pooling their skills, they paint a complex and harrowing portrait of a complex and harrowing person. But their goal is not an evening of reasoned docudrama. Rather, they see Nixon and his fallen state in terms of melodrama veering toward psychodrama. Mixing fact and speculation, empathy and accusation, they condense him and his history (or their idea of it) into about 90 minutes of florid theatricality - turning their subject into a laboratory specimen and their audience into second-hand voyeurs.

The setting is Nixon's study, where he dictates a final memoir to a cassette recorder, mingling an elaborate self-justification with memories of his childhood and career. His manner swings from maudlin to mean; his language is even fouler than the notorious White House tapes would suggest. He drinks, rants , ponders the past, and harangues the pictures on his walls.

It's fascinating to watch, in a morbid kind of way. But it's hard to pretend this is a historical study. It's an assault on the emotions, and even its climax - a charge that Nixon prolonged the Vietnam war for personal benefit - is handled in a way that seems aimed more at the feelings than the intellect.

As directed by Robert Harders, the evening includes some chillingly effective stagecraft. When the tape machine keeps playing harpsichord music instead of recording Nixon's voice, the effect is both funny and poignant, recalling the real Nixon's trials by technology. A pistol, constantly visible on a desk at center stage, is a more painful metaphor - suggesting a fearful and mistrustful streak in Nixon, and perhaps a self-destructive urge.

Despite such telling touches, however, ''Secret Honor'' is a bombastic show that tired me even as it held my interest. This unique ex-President is certainly a fit subject for theatrical research. But insights could be communicated to stronger effect (as in the Mabou Mines show ''Cold Harbor,'' about Ulysses S. Grant) through a more calm and seasoned approach - one that spends more energy probing its subject than trouncing it.