NEIL SIMON, the most successful American playwright of the 1960s-and the 1970s too, unless someone else comes along in a terrific hurry-has never had a play produced at the John F. Kennedy Center for the Performing Arts.

The reason, according to Emmanuel Azenberg, producer of every Simon play since "The Sunshine Boys," is simple: Washington, as a pre- and post-Broadway theater market, is a virtually impenetrable fiefdom governed by the whim of an all-powerful lord, the Kennedy Center's chairman Roger L. Stevens.

Azenberg's grievance against Stevens and the Kennedy Center, which also books the National Theater, led him to take a direct hand last year in refurbishing the Warner Theater as an outlet for legitimate plays.

He has already helped put "For Colored Girls . . ." and "Chapter Two" into the Warner, as general manager in one case and producer in the other, and his "Ain't Misbehavin'" comes there next month. With its limited wing space and inflexible orchestra pit, the Warner is "not an ideal theater" says Azenberg, "but it's better than the street."

Azenberg may have pressed his case against Stevens and the Kennedy Center more vigorously than most of his colleagues, but his criticisms are not his alone. A small but influential group of New York theater people share the broad view of the Kennedy Center as a theatrical monopoly reflecting the tastes (Azenberg says the "elitist" tastes) of one man.

And it is not only Neil Simon who may have been squeezed out as a result, they say, but many of the young playwrights-David Rabe, Sam Shepard and David Mamet, for example-who have been creating the biggest stir on American stages.

Stevens does not lack defenders.

"Roger does a lot of things that other people, less courageous, less wealthy, would be unwilling to do," says Bernard Jacobs of the Shubert Organization. "You can't divorce yourself from the fact that he's working for a dollar a year . . . Now he can say he has enough money, but with most people, enough is never enough." (Stevens' fortune is based on a real-estate career whose most spectacular episode was a $51.5 million deal, in 1951, for the Empire State Building).

Jacobs and others point out that Stevens is an extremely well-read man whose record as a producer (by himself, in partnership with Robert Whitehead or under the aegis of Kennedy Center Productions, Inc.) abounds with adventurous projects. Among the plays he has had a role in presenting over a 30-year career: "The Fourposter," "Bus Stop," "The Visit," "West Side Story," "Oh Dad, Poor Dad," "The Caretaker," "Rosencrantz and Gildenstern Are Dead," "Old Times" and "Wings."

One charge that even Stevens makes no effort to deny, however, is that from his hazily defined posts as chairman of the Kennedy Center and president of KCPI, the center's theatrcial producing arm, he has become the dominant figure in deciding what plays are performed there and who performs them.

"There's no theater operation at the Kennedy Center independent of Roger Stevens," says one knowledgeable colleague.

Says Stevens himself: "I sort of like to produce plays, and it seems to me that having worked for nothing in that place for the last eight years, that's the least I can ask."

If some New York producers would like better access to the Kennedy Center, Stevens adds, it is because he has established an audience and a reputation for theater there. "We haven't built that prestige up because we have done everything so badly," he says. "How long would we have prestige if we kept saying yes to everybody?" Waiting for a Call

The history of Azenberg's discontent goes back five years, to the occasion when Simon's "God's Favorite," as Azenberg reconstructs it, was "bounced out" of the Eisenhower after it had been tentatively, verbally booked in. And in 1976, Azenberg says he was turned down flat when he tried to arrange a booking for Simon's "California Suite."

Then, about a year ago, according to Azenberg, he talked to Stevens more than once about booking Simon's "Cahpter Two" into the Eisenhower Theater, and Stevens said he would get back to him.

"I'm still waiting for that call from Roger Stevens," he says. "And mind you, there were still empty slots on the Kennedy Center schedule when this request was made on 'Chapter Two." . . . There were four openings at the time, and God knows it hasn't been the best of seasons at the Eisenhower Theater.

"I feel burned and insulted," says Azenberg. "How does Neil Simon get shut out of the Kennedy Center? What reason? Why don't I have someone to talk to about that?"

Roger Stevens does not remember his conversations with Azenberg precisely as Azenberg does-he cannot remember any conversation about "Chapter Two," he insists-but "it all stems from the fact that I wouldn't take 'California Suite,'" says Stevens, "which I'd have been happy to do if it had been a good show."

Stevens does recall a time when he wanted "The Sunshine Boys" for the Eisenhower, but couldn't get it. "Where was Simon when we needed him?" he asks. "He went to the National Theater because he could get a little higher gross?" (The National has a seating capacity of 1,682 comparted to the Eisenhower's 1,104.)

"I don't know who Manny Azenberg is that he should be telling us what was ought to do," says Stevens, a man with an equally excitable, although usually short-lived temper. "Are we supposed to get out of producing if Mr. Azenberg wants us to?" Stevens' Anioms

Like other Stevens critics, Azenberg refuses to accept two key but subtle axioms in Stevens' discussions of theater at the Kennedy Center. One is that the center, as an arts arena, is entirely self-supporting-that all the direct and indirect government money it continues to receive is just fair compensation for the expense of being a presidential memorial and a tourist stop.

(The National Park Service pays for about three quarters of the center's physical maintenance and utilities, and the center itself pays the remaining quarter, amounting to about $700,000 a year. "You can call it taxes, you can call it rent, you can call it anything that you want," says Stevens, "but you still have to pay it.")

The other axiom is that Kennedy Center Productions, Inc. is a collectively run body, not Stevens' private toy, and that it represents the center's fulfillment of a mandate to generate its own theatrical attractions.

"I don't want to sit around and run a booking house, for God's sake," says Stevens, "and the trustees don't . . . If I had my druthers, we would produce everything the Kennedy Center did."

But to most Broadway producers, the Kennedy Center represents an affluent and expanding Washington theater market-the market Stevens, perhaps more than anyone, helped build. And they want in.

Like Azenberg, producer Alexander Cohen makes no effort to hide his outrage on the subject of the Kennedy Center and Stevens.

"I don't understand as a taxpaying commercial producer why the theater isn't available to me . . . Why we should be exempted from playing there except at the pleasure of one man?" he says.

Cohen, now hursing the Richard Rogers/Liv Ulmann, musical "I Remember Mama" toward its Broadway opening, says he has tried, without success, to put four of his productions into either the Eisenhower or the Opera House-not only "Mama" (which went to Philadelphia instead), but Marlene Dietrich's one-woman show (which played three performances at the Opera House under other auspices), O'Neill's "Anna Christie," with Liv Ullmann, and a revival of the musical 'Helzapoppin'" (the last two played at the National).

Why did the Kennedy Center choose to forego all these opportunities? The official reasons varied, says Cohen, but in general, "they don't want other people's attractions-not if they have anything of their own."

Stevens might agree with that generalization. He might have problems, though, with Cohen's description of most of the Kennedy Center's own fare as "the garbage they produce locally."

New York producers "try to develop a theater," says Cohen. The Kennedy Center "seems to be disinterring a theater . . . The classic revivals that they do [the word 'classic' is muttered with perceptible sarcasm] should give way to new American playwrights.

"The theater is going in a different direction. 'Buried Child' just won the Pulitzer Prize. Sam Shepherd is what's happening to the theater, not Somerset Maugham [a reference to a revival of Maugham's "Home and Beauty' directed by Jose Ferrer, which opens June).]"

For the Record

Perhaps we hear the sound of clashing personalities in this dispute. But only those with very short tempers, very secure positions or both, says one New York producer, are willing to put their complaints against the Kennedy Center on the record. The dissatisfaction, he adds, may run wider and deeper than the public expression of it.

The patented Roger Stevens revival formula-never do a revival without a big star and, conversely, if a big star wants to do a revival, don't ask too many questions-is a common topic of discussion when New York producers get to talking about the Kennedy Center.

Noel Coward's "Present Laughter" has played the Eisenhower twice, for example, with Douglas Fairbanks Jr. in 1975 and Peter O'Toole in 1978.

"Washington may not believe it," says one New York producer dryly, "but it's possible to do a good production of 'Present Laughter.'" Stevens says he was reluctant to offer the play twice in so short a period, but felt he had to bow to O'Toole's choice. He expected to take a financial bath the second time around, he adds; as it turned out, ticket sales were a pleasant surprise.

Allegations of Anglophilia and Anglophobia also manage to find their way into almost any conversation about Stevens as producer or booker.

"You'll always find an extraordinary amount of English plays in there," says Azenberg. "That is also what really infuriates me. You can book those plays in there but you can't book Neil Simon."

Stevens says it isn't his fault that "the best authors right now happen to be English." If the domestic Shepards, Rabes and Mamets had the aroma of the imported Pinters, Stoppards and Ayckbourns, they would be on display at the Kennedy Center, too. That, in short, is Stevens' explanation for the strong British presence at the Eisenhower; but he also points out that he has taken a sustained interest in the career of at least one young American playwright, Arthur Kopit, with "Wings"-a commercially unpromising venture that ended a short, unsuccessful Broadway run last night-as the widely celebrated result.

Azenberg and Cohen seem to feel they have burned their bridges to the Kennedy Center, at least for now, and can afford to shower artillery in its direction from afar.

Some of their complaints, however, are echoed in more mild-mannered form by producer Elizabeth McCann (co-responsible for "Dracula," "Sherlock Holmes" and "The Elephant Man," and a busy road manager as well as producer). McCann has done recent business with the Kennedy Center and aims to do more.

Stevens is "perhaps a little conservative or old-fashioned in the things that he produces," says McCann, although adding, "I'm not sure that isn't the right thing for Washington.

"Roger's over-all producing record would indicate that he should broaden his vision of directing and acting a little bit . . . He should reach for the young director." And, she says, "my general feeling is that Roger does not delegate well. Getting Roger to confirm dates is a major undertaking."

On "The Gin Game," which McCann's office has been handling during its national tour, "we had three or four different dates in Washington before we were through . . . Roger had forgotten that there was some kind of tribute to Frnace bang in the middle of our schedule."

On the other hand, says McCann, Stevens' position poses peculiar problems. "He's got a very large complex there and he's got to keep production going constantly . . . He could probably run 'Chorus Line' at the Opera House for six months (financially), but he can't (politically).

"He'll produce Deborah Kerr in 'The Last of Mrs. Cheyney,' which you can criticize," says McCann, "but it's a little like saying to somebody, 'Why on earth would that girl marry that boy,: and the answer is that nobody else asked her that week." Stevens, admitting the unfortunate tendency of plays to date badly, nevertheless defends "Cheyney" as a "great classic" and Kerr as a "great star."

An old theater hand who has worked on several Kennedy Center productions breaks into uncontrolled cackling at the charge that Stevens does not delegate well.

"That's a bit of an understatement," says the old hand. "Basically, Roger's the name of the game, so everything good, bad or indifferent is a reflection of Roger's personality."

But Stevens is not the sort of producer who involves himself deeply and daily in the progress of every show, according to colleagues. One producer attributes the failure of the Lerner-/Lane musical "Carmelina" partly to Stevens' tolerant, hands-off style.

"You hire a playwirght, a bunch of actors and a director and you stop by on opening night and say 'Well done!'-and it's not enough," says the producer.

Another producer carries this criticism a step further. "Basically the Kennedy Center is a packager of a creative product that originates elsewhere," he says. "The real issue is not how the Eisenhower is booked out why it's booked . . . The fundamental mission for the Kennedy Center should have been to have created a company of its own. Putting money into shows is not the same . . .

But the idea of a resident company, widely anticipated before the Kennedy Center opened, is now a financially impractical one, according to Bernard Jacobs, who recently helped the Kennedy Center negotiate a new contract with its Terrace Theater stagehands. "The moment the Kennedy Center started to operate and they perceived what the operating conditions were and what the union contracts were, they knew that they couldn't do things just for there," says Jacobs.

The Kennedy Center's union contracts are yet another cause of frequent and bitter complaint. "The labor conditions can only be said to have been drawn up by a cretin," says Cohen.

Stevens himself, with typical disarming candor, says "we couldn't afford a strike. We didn't have any money. We didn't have any money. We didn't have any reserves." These days, he adds, "they keep me out of the union negotiations-they say I'm too soft." (Another factor, he concedes, is that if he sits in on negotiations, "it leaves them with nowhere go.")

Stevens will defend his record vigorously when it is questioned, admitting an occasional error in the process.But as a businessman, he operates on the basic theory that history should be left to historians-a theory Stevens' erratic memory makes it all the easier for him to follow.

While Joseph Papp may once have criticized him for the scarcity of black plays at the Kennedy Center, Stevens is happy to contemplate a deal with Papp now that he has a new theater, the Terrace, to fill. And while he brushes off the charge that he has failed to exploit the talents of a new generation of directors-"the Arena does a lot of this and why should we copy it?" he asks when several names are mentioned-he also talks about the possibility of hiring Arena's David Chambers to direct a play at the Kennedy Center.

Whatever their criticisms of Stevens and his complex, few theater people will pass up the chance to work there. Azenberg says he can made more money as a producer at the Warner than at either the Eisenhower or the National, assuming identical levels of ticket sales, because of the Warner's cheaper overhead and its contract with a less well paid union of stagehands (Washington, in an anomaly left over from segregation days, has one predominantly white and one predominantly black stagehands' union).

But the Kennedy Center's substantial Theater Guild subscription-13,000 member's strong-and its phenomenal rate of total attendance-over 80 percent-are powerful compensations, unless a play comes here as a guaranteed hit. When all the factors are factored in, "if you had your choice, you's probably go to the Kennedy Center anytime," Azenberg concludes. CAPTION: Picture 1, no caption; Picture 2, Neil Simon, center, on set of "Chapter Two."