Playwright William Gibson has no difficulties picturing the day when "The Miracle Worker," his celebrated 1959 drama and "Monday After the Miracle," his newest effort for Broadway stage, will be playing back to back.

After all, the former, which has acquired a reputation as one of the contemporary theater's more life-enhancing experiences, depicts the arduous education of the savage young Helen Keller at the hands of Annie Sullivan, the gifted teacher who led her out of deafness and blindness into the light of civilization. And "Monday After the Miracle," set 20 years later, is about to show the theater-going public what happened to those remarkable beings 20 years later. A natural double bill for an industrious repertory company somewhere.

Gibson, however, balks when the word "sequel" is raised. The great forbidding growth of eyebrows that extends across his otherwise pleasant face in a nearly unbroken line bristles perceptibly. The term has been brought up before, one gathers, and Gibson would just as soon lay it to rest once and for all.

"I resist calling 'Monday After the Miracle' a sequel," he says. "It's a different play entirely and it comes out of a quite different period of my life. Certainly it has characters who bear the same names. But in 'Miracle Worker,' Annie was 20, and here she's in her late thirties and forties. This is a play about her marriage, with Helen in the house. So it becomes, in effect, an odd kind of triangle play. But it's also a play about parents and their child -- their grown-up, needy child. The reason I resist having people think of it as a sequel is because the joyful affirmation that they got out of 'A Miracle Worker' is not what characterizes this play. I don't want people expecting more of the same."

Whatever darker strains it may embody, "Monday After the Miracle" attracted considerable attention last spring when it premiered at the Spoleto Festival in Charleston, S.C.. Arthur Penn, who staged "The Miracle Worker," was back in the director's seat, and the cast list was headed by Karen Allen as Helen, Jane Alexander as her indefatigable mentor, and William Converse-Roberts as John Macy, the 25-year-old former Harvard professor who comes into their entangled lives, initially to edit a series of articles that will become Helen's autobiography. Time magazine proclaimed the production "one of those blazing bonfires that keep serious theater inextinguishable" and advised Broadway to take note. Now with that same team, Gibson's drama is gearing up for the big assault on New York. (On Friday, it begins a 5 1/2-week tryout in the Eisenhower Theater.)

Helen Keller has always been what Gibson calls the "headline stealer," a woman of such remarkable achievements that she overshadowed the teacher who made them all possible. "The Miracle Worker" is invariably referred to as "the play about Helen Keller" and Gibson's patience has long since been tested to the breaking point by people wanting to know how he got interested in her. "I was never interested in her," he has written elsewhere, "the play is about her teacher, and for that reason is not named 'The Miracle Workee.' "

"I read history all the time," he explains during a break in the New York rehearsals, "and I'm always coming across some wonderful story and finding myself saying, 'I've got to tell this story to somebody.' I had that feeling about Annie Sullivan, when I first read her letters. I thought, 'Nobody knows about this gal.' Nobody really did. After Annie was succeeded by Polly Thompson, people didn't know Miss Sullivan from Miss Thompson. So that's part of the impulse: To tell these marvelous stories.

"But I always respond to a story that corresponds to something that's going on inside me, because I think all art springs from that need to work out inner conflict and find a form for it. And Annie has always been a symbolic person for me, symbolic of some aspect of my life."

Gibson has installed his lanky frame on a folding chair in an empty hall in the posh rehearsal complex on lower Broadway that Michael Bennett bought and renovated with his "Chorus Line" profits. Across the corridor, musicians are running through the accompaniment for "Good." Further away, members of the "Dreamgirls" company are doing brush-up work. Gibson adjusts the plastic car seat he carries with him to make the various chairs of the world reasonably form-fitting, crosses his feet, which are sporting thick wool socks and sandals, and pursues his thought, oblivious to the distant tumult.

"I'm faithful to Annie and Helen in every detail possible. I have to try to justify them as standing on their own two feet, as independent people, because no one's going to give me two cents for what's going on inside my own head. But I always felt 'The Miracle Worker' was something more than most people took it for. It's a parable about the struggle of the artist with his raw material. In that play, Annie saves Helen, but Helen also saves Annie, by which I mean that the artist rescues the raw material, but the raw material also rescues the artist."

If "The Miracle Worker" portrayed the positive side of the ongoing dialectic between creator and creation, "Monday After the Miracle," like most mornings after, explores the shadowy, equivocal side. On the surface, it depicts Annie's attempt to reconcile her marriage to Macy with the magnificent obsession of her life, which was Helen. But Gibson likes to look at it in larger terms, as well.

"I was interested in what happens to the artist who finds that his activity is in contradiction to the everday human commitments he may want to make," he explains. "Artists are terribly self-absorbed, narcissistic people. They live for those obsessive, partial discoveries of themselves in their art and it's very hard for others to deal with some of the horse---- they hand out. But the artist also needs people -- he needs a wife, and children, and friends and so on. That conflict is the underlying theme. Anyone with a mission has experienced it. It's as true for automobile manufacturers, I suppose, as it is for artists.

"At the time I wrote the original TV version of 'The Miracle Worker,' I had a 4-year-old son, and my wife was pregnant. The writing took me about six weeks -- half of which was before the birth of our second son, half of which came after. I was working part time, going down to the hospital to visit my wife and new child, wiping dishes and doing housework. The whole sense of growing life in the house was a very necessary part of that script. I don't know that I could have written it at another period in my life.

"Naturally, 'Monday After the Miracle' is bound to be different. I no longer have the youthful optimism I had 25 years ago. I don't know anyone of my generation who does. Kids grow up and you see what monsters they become on you. More adult experiences have to be integrated into your outlook. The simple process of getting older has a certain darkening effect. I'm walking hand in hand with death a lot more. I've written about a lot of historical figures. But they've all had this value for me: they are impersonal stories that allow me to work out something personal within myself."

Gibson's interest in the psychological ramifications of art extends to his wife, psychoanalyst and biographer Dr. Margaret Brenman-Gibson, who after 15 years of research and writing recently brought out the first of two projected volumes on the life of the late Clifford Odets, a family friend. While Gibson likes to joke that he should receive "a Nobel or some kind of prize" for sitting around patiently while his wife devoted herself to another playwright, he recognizes that her work has also been his salvation, as well. Every day, he disappears into the outlying shack on their property in the Berkshires -- what he calls "the most interesting room in my life" -- to write, answer letters or sometimes "just sit and feel sorry for myself."

"If I didn't have a wife who was able to do the same with her work, I'd be in great trouble. Some women would just sit and ask, 'When is he going to come out? I'll shoot him when he does!' " Gibson laughs.

At 68, he looks rather like one of those craggy backwoods outfitters who take tourists down the rapids in Maine. When "Golda," his unsuccessful play about the Israeli prime minister, tried out at Baltimore in 1977, he settled into Patapsco State Park for the duration of the run, preferring his tent to "a stuffy hotel room." He'll be checking into a hotel during the Washington tryout of "Monday," but fully intends to disappear for a weekend or two of backpacking in the Shenandoahs. While he's been dutifully attending rehearsals in New York and contributing the kind of fine tuning that "will make the machine run without clanking," it's not a process that much enchants him.

"I love to write plays," he says. "But what I hate is the rehearsals, the production work. By the time a show opens in New York, I'm saturated with so many associations of trepidation, anxiety, disappointment that, whatever the positive returns, the play is finished for me and I'm glad never to have to go back and look at it again. I never really liked 'The Miracle Worker.' Oh, I knew it was a good story and I was determined to be as good a secretary to that story as possible. But I was very taken aback by the response. I never thought it was much of a play until I saw it a couple of years ago in South Africa. It was being performed in Afrikaans and I didn't understand a word of it. But I thought, 'From the outside, this looks like a good play.' "

After a decade of mostly unacknowledged writing, Gibson broke through in 1957 with the TV version of "Miracle Worker" on Playhouse 90, which remains one of the classic television dramas. It was followed quickly by "Two for the Seesaw," the stage version of "Miracle Worker" and the sale to films of "A Cry of Players," his drama about young Will Shakespeare that didn't get filmed but eventually was produced on the stage a decade later at Lincoln Center. While other playwrights had to scurry out to Hollywood to pay the bills, the triple whammy made Gibson financially secure and allowed him to pursue his career in the theater unimpeded.

It's just as well. Movie and TV scripts don't interest him. "They're too easy," he sniffs. "With a camera, all you have to do is make one point and then, snap, you can go to China. In the theater, you're working inside a time and space unit. You can't move laterally. You can only move vertically. It's much more challenging."

"To this date, "Miracle Worker" and "Two for the Seesaw" remain his biggest hits and continue to feed him royalties. Gibson acknowledges that some of his subsequent works -- "The Butterfingers Angel" and "Goodly Creatures," for example -- were undertaken with no commercial expectations at all. Both, however, have been given remarkably effective productions by the tiny Round House Theatre in Silver Spring, which pleases Gibson greatly. He came down and worked with the youthful non-Equity company each time and considers the experience in no way a fall from the more garish heights of Broadway.

"The paradox of writing for the theater is that it is possibly the only art form that is also big business," he says. "If you write a string quartet, there's not much chance of selling it to Hollywood. Consequently, you can approach things from two viewpoints. There's the extreme end of commercialism, in which case you're out to make a product that will sell. You do all you can to make it as marketable as possible, which means you're always thinking about the audience. Or you can say the theater is an instrument, which I will use to express some of my knowledge of life. Then your orientation is much more internal and you're interested in the ideas you have to communicate, even though you're not sure a need for them exists out there."

He unfolds his legs and stretches out the cricks that have gathered in his neck.

"Of course, the artist always wants to make a dollar. And the man who makes a dollar wants to be thought an artist. But the theater has always been more of an expressive arena than a money-making place for me. Basically, I love the manipulation of language with a pencil and a paper. I love moving sentences around. I've really never been competent at anything else."