In real life, Alan Alda chooses his words quite deliberately. Compared to the rapier wit displayed by Captain Hawkeye Pierce in TV's "M*A*S*H," Alda's style is more like a saber, but no less sharp.

Stage 9 at Twentieth Century-Fox in Los Angeles is deserted for an hour as the crew of "M*A*S*H" takes lunch. Alda, still in his green fatigues, has put down a metal spoon and a white saucepan lid that he was banging in a drunken party scene. In the studio commissary, he is sipping on a glass of white wine and easing into conversation about "The Seduction of Joe Tynan" -- the movie he has written and starred in.

The film, originally entitled "The Senator," is about a fictitious Sen. Tynan of New York who is captivated by power and success as much as he is by the charms of an attractive woman. Though its setting is the Washington political world of a Kennedyesque politician with his sights on the White House, the movie is not, Alda insists, a political one.

"The movie is really about the danger of losing touch with what's personal," he says. "Anybody faced with success has to deal with the problem of ditching his or her family to get to that success.

"Most men feel that family kind of works on its own steam, and you can keep the family on a shelf for a while, while you do this other so-called truly important work of your business, your career. And when you come back to them, they'll still be there. Well the fact is they're either not there, or they're different people when you come back to them."

It is a dilemma that has affected Alda during his rise to film success. But he insists that the movie is not autobiographical.

"The truth is that I'm successful in my field, and you can't be successful without having to face the question of giving to Caesar what's Caesar's, giving to your soul what's your soul's," he says. But that is as revealing about his personal life as Alda will get -- he closely guards what privacy he has.

The strains on his own family have clearly eased over the years. There were the times when, during the filming of "M*A*S*H" (now in its eighth season) he would fly back every week from California to New Jersey where he lives in a small town with his wife Arlene and his three daughters, Eve, Elizabeth and Beatrice. Aged 18 to 20, they are all in college, and Alda now lives with Arlene in Bel Air during the six months of the year when "M*A*S*H" is being shot, and in New Jersey the rest of the time.

If Alda is not the libidinous wise- cracker that viewers of "M*A*S*H" might expect, there is still a humorous twinkle and a hint of latent mischievousness.

He is a dampened version of his screen persona: His hyped-up, energetic metabolism in front of the camera slows down like a 45 rpm record played at 33 1/3, and Alda becomes thoughtful, at times unexpectedly ponderous.

The lanky, 6-foot-2 actor was born in New York City in 1936, the product of a show-biz family. He is the son of Robert Alda, the stage and screen actor known for his role as George Gershwin in "Rhapsody In Blue." In the 1940s, living in Hollywood where his father was under contract to Warner Bros., the younger Alda on occasion teamed up with his dad to entertain soldiers at the Hollywood Canteen, and appeared with him on the stage.

After finishing high school in New York, Alda attended Fordham University. His junior year took him to Europe to study at the Sorbonne, but he spent most of his time traveling, appearing with his father on stage in Rome and in television productions in Amsterdam.

In the early 1960s, he acted on the New York stage and appeared in NBC's short-lived satirical review, "That Was the Week That Was." He played in a number of movies toward the end of the decade, but did not become a national celebrity until "M*A*S*H" premiered in September 1972. He has since starred in several TV movies and two films, "California Suite" and "Same Time Next Year."

While "Joe Tynan" draws on Alda's personal knowledge of the strains between career and a family, it also relies on his experiences politicking for the past six years as an ardent champion of the Equal Rights Amendment. His campaign has left him somewhat embittered and cynical toward politics and politicians. "I think I'm more cynical having done politics a little bit than I was before I got into it," he says. "I used to campaign for (Sen. George) McGovern and (former Sen. Eugene) McCarthy.

"I could campaign for an issue now -- but I don't know if I could campaign for a candidate.

"Candidates and office-holders tend to be a collection of appearances rather than people with substance. I know there are exceptions to this and I don't want to offend everybody in Washington by (saying) that everybody there is full of hot air. It's not true. But it's jockeying of images rather than the arguing of the case that I see constantly," Alda says, and offers some examples.

"I've seen people offer their vote for the ERA for some consideration that has nothing to do with whether or not it would be good for the people they represented. If a woman would go to bed with them, they would vote for it. In one case, if a legislator could get his son's high school marching band in the inaugural parade, they would vote for it. Another one said he would vote for it if some movie stars would call him up. Another said he would vote for it if he could get a free trip to Washington so he could meet the president."

His encounters with politicians, "a shelf full of books" and advice by Washington Post writer Richard Cohen enabled Alda to add insightful touches of realism to "Joe Tynan," his first screenplay. In the film, a mechanical letter-writing machine spews out letters to constituents complete with signatures provided by automatic fountain pens. A campaign consultant coaches the senator on his speech delivery, and a senile senator played by Melvyn Douglas confesses, "After a while, you forget what you're here for. Getting clout and keeping it is all that exists."

While the ERA and pro-feminist issues remain Alda's political passion -- he was a member of the National Commission on the Observance of Women's Year, and has written for Ms. magazine -- he has also taken public stands when he thought freedom of speech was threatened.

Recently, after the California State Senate rejected the appointment of Jane Fonda to the State Arts Council, Alda's name appeared with 284 others on a full-page newspaper advertisement condemning the state senate, and pledging to "fight any resurrection of the specter of McCarthyism." And after the University of California at Davis struck Fonda's name from its list of nominated graduation speakers, Alda withdrew his own from the list of six remaining nominees.

"If Jane Fonda is turned down as a speaker because she is, 'a little bit too controversial right now' -- that's what they told me when I called the university -- then she could be turned down for a part on a television show because she's a little bit too controversial right now," Alda explains indignantly. "This stuff has to be stopped while it's still stoppable, so that even though you might risk over-reacting, it's worth the risk."

Although outspoken, Alda shies away from the political spotlight. "I don't find any excitement in politics," he says. "I don't enjoy it, but you can't get away from it. We live in a political atmosphere. Everything that everybody does affects everybody else. It's like taking out the garbage. It's something that has to be done.

"The Seduction of Joe Tynan" opens nationwide tomorrow, and in Washington a week later.

But Alda is already at work writing his next movie. It will be entitled "The Four Seasons" and will be a comedy about the friendship of three couples. If all goes well, he says, he will direct it and act one of the parts next spring. While "Joe Tynan" is a drama with some comedy, the next project will be a comedy without much drama.

That mixture of humor and seriousness has made Alda a respected Hollywood personality. The recipient of Emmy awards for acting and directing "M*A*S*H", he has also twice won the popularity contest of The People's Choice Awards.In addition, last week he received three more Emmy nominations -- for writing, directing, and acting in "M*A*S*H" episodes.

It is ironic that Alda, a pacifist, should achieve his widest recognition from the Korean War. But he says he has turned down parts in conventional war movies that glorified combat and is comfortable in a program that sets life-saving doctors in a battle zone. Is "M*A*S*H" another example of Alda's reputed cynicism?

"I don't really value cynicism very highly," he says, 'and it's not really a true picture of how I feel.

"I have a healthily jaundiced eye toward what I think politics is. But that's balanced by the fact that I think there's hope for all of us in realizing that there is somebody at the end of every decision we make in every business, not only politics.

"When they make a car with a gas tank that blows up, somebody's going to be in that car, and it's only understanding that there's somebody at the other end of your decision that will keep this great number of us from doing one another in."