IF A PLAYWRIGHT must turn 65, where better than on the road, with a new play headed, amid all the usual confusion, for Broadway?

1arthur Miller is spending his first day of Senior Citizenship in Baltimore, and he seems pleased about it. While his wife (photographer Inge Morath) takes promotional pictures in the auditorium of the Mechanic Theatre, Miller sits in the adjacent bar, his feet propped up on a neighboring chair, shifting positions every few minutes as he talks, in free-flowing, slightly delicate Brooklynese, about his career, the state of the theater and the effect of the Depression on the American people -- which happens to be the subject of "The American Clock," his new play.

He is a voluble 65-year-old, obviously glad to be back in the theater where "the author dominates" or "if I don't dominate, certainly nobody is over me. Willy-nilly, it will work or not if I make it work or not. And the labor is such that I'd rather have it that way, instead of putting my fate in the hands of some person who may or may not be able to carry it out."

He had no such feeling of control over his recent TV script, "Playing for Time," a $2-million-plus production that would have cost $7 million or more to do right, according to Miller. "On the whole, I was very proud of it," he says, "but nevertheless, I'm publishing the script because for economic reasons some stuff never got shot . . . Perhaps, it wouldn't have been any better, but the top of that cathedral was missing."

So any TV producers with thoughts of wheedling another script from Miller can forget it. And he has had his fill of screenwriting, although it has been 20 years since "The Misfits," his last movie. "To write a movie, you've gotta consign yourself to being the fifth wheel of the vehicle because fundamentally the control of this thing, once that camera goes, is in the hands of the director."

Yet for a man who calls the theater home, Miller doesn't often find himself in the audience. Asked to identify a few contemporary playwrights he admires, he recalls, with considerable difficulty, the not-so-contemporary name Edward Albee -- one of the few currentplaywrights who have "hung around long enough," says Miller.

And what of Michael Weller or David Rabe or Lanford Wilson?

"I was talking to Joe Papp the other day at a meeting that was called for Harold Clurman's passing -- a memorial-- and we were standing in Schubert Alley, and there were all these dozen posters, and I said, 'You know, I haven't seen one of these shows.' And Papp said, 'well, that's because you're not in show business.' And I think there's something in that. My references are not inside the theater. Frankly, I never went to the theater a lot, even when I lived in New York all the time."

He now lives in the green hills of Roxbury, Conn., where, despite being one of the most famous and acclaimed writers in America, Miller seems conscious of a certain cultural isolation. It has been eight years since his last Broadway play, "The Creation of the World and Other Business," and 12 years since his last success, "The Price." He worries that the theater -- perhaps the country in general -- is no longer receptive to his idea of a play, in which man's personal, social and economic selves are seen through the same wide-angle lens.

"Sometimes I don't know why I'm still doing all this nonsense," he says, "but I got stuck with it, and that's what I'm doing . . . Yeah, I get where it doesn't seem worth all the labor and the effort, in view of the trendiness of criticism, which can kill you in the theater . . . "

Playwrights also have their trends, he acknowledges regretfully. At a midwestern university a few years ago, he asked a conclave of aspiring dramatists to describe their styles of playwriting, "and one guy described what I suppose was the Beckett school of play. And they began to grin because they were all writing in fundamentally the same style. And I said, 'Isn't it amazing how people coming from different parts of the area all end up writing in the same style?' I can't believe that's a good idea."

The worry has immediate relevance because "The American Clock is a kaleidoscopic, semi-documentary look at the Depression, with unusual emphasis on material matters and the individual's relation to his government. "I'm trying to create a relationship which is theatrically elegant," says Miller, "between the great public drift of that time and the people on the bottom."

To Miller, the '30s were a cathartic moment in the American people's sense of their possibilities, individually versus collectively. "People could have lived -- before Roosevelt's time -- substantially a whole lifetime without ever coming into contact with the United States government in any way, shape or form. It was delightful."

He chortles, and continues: "So the whole idea that people were dependent on the government was a brand new notion as a result of that calamity, with all the good and bad that that entails . . . For most Americans, revolt was out of the question because fundamentally, they blamed themselves. There was a lot of rhetoric about the system failing, but an inch below that rhetoric was the idea of the self-made man, the idea of society as an arena into which brave men and women, mostly men, ventured in order to secure wealth, power, fame or a living."

Miller sees the form of "The American Clock" -- encompassing characters and events that don't directly relate to each other -- as a complement to its substance. "Its a pre-bourgeois structure," he says. "Its Shakespearean. Before the middle class took over everything, man was not separated into his various compartments quite as much. We weren't ashamed of money and the economic part of man's life . . . And It wasn't thought necessary to separate what we call psychology -- which is fundamentally parental relationships and sexuality -- from the power relationships."

These days, he says, characters in the theater "don't work for a living. Once the curtains part, these people seem to suck off the teat of some theatrical cow."

For the first time in his 36-year career, he launched this play outside the Broadway arena -- at the Spoleto Festival in South Carolina last March. "Because it was an experiment," he explains. "And I'm still tinkering."

He deliberately chose a director who had worked away from New York (Daniel Sullivan) in the hope of achieving a production as free of Broadway trends as the play itself. (Sullivan withdrew from the production last Wednesday, and was promptly replaced by Vivian Matalon, the director of "Morning's at Seven", and "Brigadoon." Sullivan was said to have felt he "could not longer serve the play.") But Miller says the pre-Broadway tour (rather than a preliminary production at a resident theater like Arena Stage) is still the best route for him, because that way he has the widest pool of actors to choose from. "See, there is a problem," he says. "I write acting scenes. People have to be able to act."

The Baltimore run ends next weekend,and then it is on to New York, and for Miller, on to the writing of his first musical, "Up From Paradise," and an evening of two one-act plays, "Elegy for a Lady" and "Some Kind of Love Story."

Miller yawns -- discreetly. "I'm sleepy as hell," he says, rising for the imminent resumption of rehearsals in the hall beyond. "This is no business for people who like to sleep."