RALPH ALLEN took up residence at the Kennedy Center last week with the ambiguous, low-keyed and temporary title of "theatrical consultant."

But his job will become permanent, and important, if things work out to his and chairman Roger L. Stevens' mutual satisfaction.

"I would hope he would take charge of the theater part of this operation -- I've got too many other things to do," says Stevens, who means to celebrate the Kennedy Center's 10th birthday by launching, at last, a theater company of his own. He describes Allen, a 47-year-old academic and co-creator of the musical, "Sugar Babies," as "very experienced, very knowledgeable" and living proof that "people in universities do know something about theater sometimes."

"The job is evolving," says Allen, more cautiously. "I'm here to do whatever Roger Stevens needs me to do." That meant, last week, flying to New York to monitor rehearsals of "Sarah in America," a two-character play starring Lilli Palmer as Sarah Bernhardt.

But Allen expects to spend much of his time laying plans for the new company, intended to fill 36 weeks at the Eisenhower Theater next season. No one is saying yet how the company will be structured, or who will act in it, or which plays it will perform, but if Allen's background and enthusiasms are any clue, the range could be a wide one.

"I've had an odd career," says Allen, and a list of his trades -- teacher, theater administrator, historian, Broadway-musical author and dirty-joke collector -- bears out his claims to oddness, which are further confirmed by the businesslike cut of his jib. In a three-piece charcoal suit and black-rimmed glassed, he looks more like a corporate lawyer than a man of the theater, and his personality has its lawyerly side too. Despite an unassuming, "What-do-you -think?" style of conversation, there is evidence between the lines of his resume that this is a man with considerable persuasive abilities.

Some examples of Allen at work:

Between 1972 and '74, as head of the speech and theater department at the University of Tennessee in Knoxville, Allen helped convince a group of donors including ex-movie director Clarence Brown to build a theater and found a professional company on the university campus.

In 1973, when Allen came to Washington for a gathering of the American Theatre Association and went to see Roger Stevens on ATA business, Stevens, hearing of the plans for a theater in Knoxville, immediately volunteered to help. "Okay," he said, "you want to do that? Let me bring a play down there." The play turned out to be "Everyman" with Anthony Quayle.

To begin with, Allen and Quayle didn't get along. "He was kind of annoyed at having to be in Knoxville," Allen recalls. But when they got to know each other, Quayle decided to spend a whole season with the new Clarence Brown Company -- and did. (Among the other stars Allen lured there were Mary Martin, June Havoc, Eva LeGallienne, Siobahn McKenna and Keith Baxter.)

When Allen produced a burlesque revue in Knoxville and it failed to catch fire with Broadway producers, he outmaneuvered them. Asked to give a lecture on burlesque at Lincoln Center (a lecture entitled "At My Mother's Knee and Other Low Joints"), he invited producer Harry Rigby to attend.The lecture, drawing on Allen's huge collection of vaudeville and burlesque sketches, gave Rigby an idea (or so he thought): Why not assemble Allen's material into a Broadway show?

"Well," said Allen, "it just so happens I have a script here . . ."

And he handed Rigby the script that became "Sugar Babies," a compilation of "remembered and invented" burlesque and vaudeville routines. Allen then made four trips to the West Coast to snag Mickey Rooney as his star, a casting coup that probably helps explain why the show is still going strong on Broadway after more than 500 performances. (The road company recently folded in Boston -- "a great disappointment," says Allen. "I had gone out and bought my wife a big present on the strength of the reviews.")

"I really like low comedy and I think it has value," he says, explaining the seeming incongruity of his careers as a teacher and a dirty-joke buff. "It's unsentimental without being bitter or cynical . . . Those sketches struck me as worth collecting and worth preserving." In the same vein, he has a show in mind called "Honky-Tonk Nights," a recreation of the brand of "rough entertainment" found in turn-of-the-century downtown red-light-districts.

But he is equally passionate about Shakespeare -- for example, a production of the complete "Henry IV" cycle he saw at Stratford when he was 17. It starred Michael Redgrave, Richard Burton, Alan Badel, Harry Andrews, Hugh Griffiths and (playing Falstaff as well as directing) Anthony Quayle. h"I had never seen anything like it and I've never seen anything like it since," says Allen, who dates his decision to work in the theater from that experience.

He praises Stevens for hs "openness" and his "ability to take advantage of happy accidents" -- including, presumably, the accident of their meeting, which led to a series of Kennedy Center shows originiating in Knoxville, away from the glare of the New York theater establishment. "People find him an easy target at times," says Allen, "and they forget that he's done wonderful things -- things that are not normally productions that commercial producers would do." He cites Friedrich Duerrenmatt's "The Visit" and Preston Jones' "Texas Trilogy."

An integral part of the Kennedy Center's 1981-'82 theater plans is the adoption of a less expensive LORT (League of Resident Theaters) contract with Actors Equity, and Allen has already done some valuable persuading toward that end. Sent to New York to talk things over with Equity, he returned, according to Stevens, with a tentative okay.

Allen is vague about plans for the new company, but a few broad intentions have emerged. The company will probably do six plays. It will employ stars and non-stars alike, for varying lengths of stay. It won't tour, and certainly won't be set up to send shows to Broadway. Stevens has mentioned Alan Schneider, Craig Anderson and Louis Scheeder as possible directors, and he has spoken, at one time or another, to such actors as Hume Cronyn, Jessica Tanday and Jason Robards about participating.

And the trend toward smaller and smaller productions, with fewer and fewer people, could finally be reversed. With an ongoing company, says Allen, "You can finally do plays with a large cast."