One day during the recent Christmas rush, Isabelle Stevenson dropped by Bloomingdale's and asked a young saleslady where she could find socks for men.

"Why, Mrs. Theatre!" the woman exclaimed. "I'll tell you where to find socks."

That extravagant appellation is not far off the mark, either. As president of the American Theatre Wing since 1966, Stevenson is one of the most tireless workers in the vineyards of theatre. Not only does her organization pass out the Antoinette Perry "Tony" Awards every June for achievement in the theatre, she's forever tilling the fields, nurturing them to find new audiences.

"I think our salvation has to be younger people coming to the theatre," she contends. "You got a younger audience with Tommy. They'll pay for that once-a-year-event rock concert, but that's not enough for theatre. They have to go to the theatre the way they go to movies, and they won't do that unless they know theatre well enough to spend money on it."

Bob Callely, the Wing's executive director, seconds that motion and has done something about it. "When I came here, there was a program called Theatre-in-Schools where we took performers and the occasional director around to schools, but it wasn't extensive. I talked to folks and increased the concept, so we could touch every single part of what working in the theatre is all about."

In addition, the Wing has a hospital program, which last year presented a record 80 shows in hospitals, nursing homes and AIDS centers around the New York area. Plans are also already under way for the Wing's spring luncheon a civilized "roast," pitched at the Plaza. At Christmas the Wing plays Santa to various theatre organizations around town, such as the Signature Theatre Company, which is currently presenting a season of Arthur Miller plays. In December, a record $101,000 was divvied out among 44 different groups plus an additional $5,000 to the Lincoln Center library for a program of conversations with people in the theatre.

Seven hours more of theatre talk come every spring and every fall via the Wing's CUNY-televised "Working in the Theatre" Seminars, where theatre artists get together and "talk shop" before a live audience.

There has already been some discussion of pegging the next production seminar to The Lion King, which completes a cycle of sorts in Stevenson's mind. She remembers some years ago presenting its director, Julie Taymor, a Wing award for an Off-Broadway effort. The check was only for $100, but Taymor clutched it happily like manna from heaven, which it was.

"I love what I do," Stevenson freely admits. "I love theatre, and I love taking it into the schools. When you see these enthusiastic students, then you see [someone like] Vanessa Redgrave staying afterward to talk to them it's great. Their press agents are champing at the bit to hurry them on, but they want to listen to the questions. Acting's really a noble profession and a great one."

-- By Harry Haun