Lady Irene appears at the John F. Kennedy Center for the Performing Arts from three to six nights a week, a schedule she has maintained ever since the Center opened.

"I haunt the Kennedy Center," is the way she puts it.

If you haven't caught her onstage - and there has been ample opportunity to do so during the Opera House's 1976-77 season - you may have glimpsed her in the audience or at the stage door. Sometimes, she is in all three places in a single evening: on stage for Act I, in the audience for Acts II and III, and waiting at the stage door after the curtain has gone down.

"Lady Irene," is actually a theatrical name, in that it was given to her by Kennedy Center staff members, who describe her as "extremely gracious, extremely sweet." Her real name is Florence Irene Shomshor and her real career, before she retired, was as a librarian for the Air Force.

Since she first came to Washington as a young woman entering the Civil Service, she was always at Constitution Hall, Lisner Auditorium, the National Theater. And she started planning her relationship with the Kennedy Center years before it was built.

"There was all that controversy about where they were going to put it, and I guessed correctly that it would be on the Potomac," So by the time it opened, she was comfortably ensconced in a cooperative apartment right across the street, ready for te curtain to go up every night.

Others who live alone may use television for continuous company. She wants to be out among live audiences at the very best of live performances.

She buys a ballet subcription every year, and series tickets for the Philadelphia and international orchestra. And she buys tickets for nearly every other concert and many of the plays. "There are few things I don't see."

After the performance, she would take her program backstage to be autographed. But it wasn't until recently that she conceived the desire to go on stage herself.

"I saw 'Boris Godunov' three times in one season," she reminisced, "and I saw so many people on stage that I decided there might be room for me, too."

Up until then, her stage experience had been "a recitation in German when I was 3," in her Nebraska hometown; "the leading role in 'Snow White' in junior high school," and "a piano recital when I was 17 or 18."

In Washington, she appeared in two films: a crowd scene with Cary Grant in "Houseboat," a job she got because extras with security clearance were requested, and she had that because of the Air Force; and a spectalor role in a Russian film made of the Hermitage exhibition here, while she got because she happened to be looking at the pictures when the film crew appeared.

But last summer, she began her career as a super at the Kennedy Center. She made her debut with La Scala, as a panhandler in the crowd scene of "La Boheme." And then she was in the Paris Opera production of "Faust," once in the crowd scene and later "on the balcony, with just two other suppers." A few weeks ago, in the American Ballet Theater production of "Petrouchka," she was the little old lady who stepped forward from the crowd, mesmerized by the Charlatan's flute.

It has been, she said, a thrilling season. "I love all the excitement, the confusion. Before, when I went to a performance, it might be lovely, but it would just fade away afterwards. These will be with me, always." (SECTION) o she has left her resume with the Kennedy Center production office, giving her age as "30 plus," and mentioning the skill of "ballroom dancing." She would "dearly love to do more, if I qualify," and has her eye on a coming production of "Carmen," where she figures "they'll need a cigarette vendor in the street scene."

Does this meanher ambition is growing? "Oh, dear no," she said. "Absolutely not. It's so relaxing just to sit there and listen to artists - I wouldn't want to have to be one. It's enough to be on stage with a great artist."

But she does have one unfulfilled theatrical dream. "I would dearly love to be in 'Boris Godunov,' rubbing elbows with all those elegant robes and beautiful jewels."