Some people in Washington don't even know there's a library at the Kennedy Center.

And who would expect one, since only a few arts centers in the nation are equipped with thousands of arts volumes and headsets enough for 30 people to listen to a Wagnerian opera before the curtain goes up.

"Come to the Hall of States," says the information operator with the ease born of repetition, "and take the elevators up to the North Gallery." There, tall glass doors open into the welcoming hush of the friendly, one-room performing arts library, not nearly so imposing as one might expect from a joint project of the Kennedy Center and the Library of Congress.

Actually, it's "teeny, tiny," admits Head Librarian Peter Fay, who describes the ambiance he tries to create as both "informal and informative."

Which is actually a pretty good description of the man in charge. Whether lecturing about music as he often does, appearing as a regular panelist on WETA-TV's "Around Town," or acting as gatekeeper to the city's premier repository of performing arts trivia and lore, Fay is an articulate guide through the information maze.

"Our job is not to be the biggest library in the world," he explains. "We're sort of the smallest part of the biggest library in the world. We're a point of entry for any researcher -- it may be for a term paper, or a dissertation, or the book to end all books on the history of ballet before 1950 . . . . Maybe you're raising money for a local arts organization, or simply a member of the general public who's always wanted to know about Beethoven . . . . The idea being, if you come through our doors, we're going to help you."

Friendly by nature, Fay describes himself in late fortysomething banter: "I'm 5 foot 11 and shrinking," and "I used to be blond, but now I'm balding." But any illusions that he is slipping into a lethargic middle age are quickly dispelled as he talks about his job.

"I am one of the luckiest people I know. I came from a musical family . . . did my undergraduate and graduate work in music, and somehow or other ended up in a library. Everybody said, 'Oh my gosh, you're going into library work -- poor thing. It's a shame you couldn't get real work.' But it's been fun."

A New York native, Fay came here in 1962 to attend Catholic University and never left. After a stint as a music teacher in Prince George's County schools, he sold music at Dale's music store in Silver Spring, where he got into answering people's questions about music, "which has always fascinated me."

That fascination found an easy outlet at the Library of Congress Music Division 20 years ago. "My favorite off-the-wall request came from a guy who was living on a commune with his girlfriend. They were living exclusively on goat milk, and he wrote to ask if we knew of any songs useful for getting more milk out of goats."

Few performing arts centers have public libraries. When they built one in New York City's Lincoln Center in the early 1960s, it was considered highly innovative. But a study for the Kennedy Center a few years later said a library was essential.

"But just as they were getting ready to open the center in 1971, bingo, they ran out of money," said Fay. "But a bunch of key people . . . including the late, lamented Lily Guest, Mrs. Marriott was another, said: 'Come on, we've got to have a library.' So they went over to the Library of Congress and said, 'You guys come on and give us a hand.' "

In 1978 Fay won the librarian post, and in March 1979 the library opened.

Fay doesn't get a lot of requests for goat-milking music anymore, but every day, he and his staff of two librarian specialists and an assistant field questions about everything from the year of Mikhail Baryshnikov's American debut to the plot of Lerner and Loewe's "Brigadoon."

The most arcane local factoids can be found here and nowhere else, Fay says, because "we take information from any source." For instance, the library has an indexed collection of every program from every performance at the Kennedy Center. "No other institution that we're aware of has been doing that kind of thing. And as time goes on, that becomes a more and more valuable collection. It's all part of our responsibility," said Fay.

And since, as he puts it, the center's "gaze extends nationwide, but its feet are planted in this community," Washington is especially well represented in the collection.

"We have a program from the first play that Helen Hayes was ever in, at the Columbia Theatre in Washington in 1906. We also have a juicy collection of interviews with people who have received the Kennedy Center Honors."

Once he gets started on Washington, Fay is off and running. "People who live in Washington always say, 'Gosh, when I came here five years ago, there wasn't anything going on in D.C. . . . Or 10 years or 20 years or 50 years. They always say the same thing.

"It used to be that our friends in New York reminded us that D.C. was not another New York; now my response is that New York is not another D.C. . . . If you look at the galleries, if you look at dance performances, if you look at theater growth in this area in the last 10 years, it's astonishing."

Fay should know. He's stayed involved in that growth. In addition to his work as librarian, Fay continues to sing, lecture and, most time-consuming of all, to appear on WETA's "Around Town."

The show's host, Robert Aubry Davis, says Fay's expertise has resolved many a heated discussion between panelists over the years. "He has an evenhanded, sort of scholarly approach to the show, which makes him invaluable for getting potentially emotional situations back on track.''

A fellow panelist, theater critic Bob Mondello, agrees. "The wonderful thing about Peter is his incredible breadth of knowledge. He comes at a play, for example, with ideas about its history, its period, as well as how it might have originally been done . . . . I mean, essentially, Peter's a librarian!"