Being a member of the Woolly Mammoth Theatre Company, says Grover Gardner, is "what saves me from drink, boredom and depression."

For actors who may be susceptible to such maladies, Woolly Mammoth would indeed seem to be the ideal preventive medicine. The theater is in the middle of its most critically successful season, with a repertory that includes "Christmas on Mars," "New York Mets" and "And Things That Go Bump in the Night" -- three offbeat, modern plays that suit Gardner, a converted offbeat, modern actor.

"In college, I did absolutely straight repertory -- up and straight head things," he says. Out of college, he contemplated a career filled with "straightforward, boring" roles.

Then he took the part of Galactic Jack in the Paradise Island Express production of Sam Shepard's "The Tooth of Crime."

"I just went for it," says Gardner. "Then I got here and all of a sudden [Woolly Mammoth artistic director] Howard [Shalwitz] said, 'I want you to play a cockroach.' "

That portrayal of Gregor in last year's production of "Metamorphosis" won Gardner a Helen Hayes nomination for Outstanding Lead Actor. He received a second nomination in the same category for his performance as Lewis Carroll in "Looking Glass."

Reacting to what it considers a dearth of good directors, Woolly Mammoth has started to develop its own. Two of the theater's current productions mark professional directorial debuts -- "New York Mets" by Ernie Meier and "Christmas on Mars" by Gardner.

"I think I have an instinct for it," says Gardner. "One of the problems I have as an actor is a tendency to direct myself too much. I have a few too many suggestions when it's not my turn."

Like other Woolly Mammoth company members, Gardner has a day job (he can be heard on more than 50 selections for Books on Tape, ABC's Classic Books on Cassette and the Library of Congress' "Talking Books" program for the visually handicapped). Working away from the theater "keeps people grounded in what real life is," he says.

"One of the dangers for regional companies that pay people full time is the neurotic, inbred feeling to acting and directing that says, 'This is our own little world and we can do whatever we want here.' "

One might have guessed that despite his success, Gardner isn't planning on running off and joining a big regional theater company. "What could they use me for?" he wonders. "I'm a somewhat difficult actor to place.

"But," he says, "I could be wrong."

Papp on Stage

Joseph Papp, producer of the New York Shakespeare Festival, will speak tonight at the bimonthly dinner meeting of the Congressional Roundtable on U.S.-Soviet Relations. Papp, who has produced such Broadway hits as "Hair," "The Pirates of Penzance" and "A Chorus Line," and Maestro Mstislav Rostropovich will address about 45 members of Congress on the topic of "Arts and Politics in the U.S.S.R." Papp has been talking with the Soviets about sending "The Nest of the Woodgrouse" -- a play by Soviet writer Victor Rozov that Papp produced and directed in New York and Washington in 1984 -- to Moscow for a possible television special to be shot there. He has also been negotiating with the Soviets about sending a touring company of "A Chorus Line" to Moscow.

'Dreamgirls' Tryouts

Open auditions for Actors Equity and non-Equity black performers for the touring company of "Dreamgirls" will be held at the National Theatre, May 29 for men and May 30 for women. Interested performers aged 18 to 30 who can sing, dance and act, should call 628-6161 for details.

Odds and Ends

"The Foreigner," the award-winning comedy by the late Washingtonian Larry Shue, became the longest running play in New York last Tuesday when it had its 655th performance at the Astor Place Theatre . . . Both Roger L. Stevens and Marta Istomin, Chairman and Artistic Director of the Kennedy Center, respectively, over the weekend received honorary degrees from