Sen. S.I. Hayakawa does it (but, his staff insists, only at home). A 43-year-old government personnel administrator does it for a lark and to improve his tennis footwork. A middle-aged lobbyist says it helps him get parts in community theater, and a 30-year-old counselor likes it for the exercise and escape.

"Tap dancing attracts people for a variety of reasons," says tap instructor Joe Jeff, 25, a slightly built, hyperkinetic dynamo who has taught his art to hundreds of potential Ruby Keelers and Fred Astaires through Washington's Open University.

"But most people take my class for one reason: They're just seen a '30s movie and found themselves doing a little shuffle on their way to the kitchen to grab a beer."

Dubbed the "wonder man" by former first lady Betty Ford, who was a student of his, the 5'7", 122-pound hoofer cuts a Joel Greyish figure in his tight red tee shirt, slinky black dance pants and owlish tortoise-shell glasses. In addition to tap dance, Jeff has taught such unorthodox Open University Courses as Social Kissing. Nursery School for Adults, Beginning Magic and Burlesque '77 - in which 50 students rode an English doubledecker bus to Baltimore's "Block" for the once-in-a-lifetime chance to walk down the runway at a strip joint.

Jeff's razzle-dazzle teaching style as as wild as the subjects he teaches, making him one of Open university's most popular instructors. He's currently turning one of his most popular classes, Teaching as a Performing Art, into a book that he hopes to have published next year.

"To be more than just an average teacher - to be a dynamic and inspired teacher - you need charisma," he claims. "To really attract your students and keep them interested you need training in dance, magic, acting and makeup." This vaudevillesque philosophy makes Jeff's tap class - an hour and a half a week for four weeks-an exciting blend of circus, school and magic show, all done to the tune of rousing George M. Cohan music.

"You see, inside everyone there lurks a hidden desire to be in a spotlight," grinned Jeff, who claims he can teach anyone to tap dance in about 10 minutes. "I run my class on a very theatrical basis, as if the MGM bus might pull up and discover a star any minute."

Jeff said his phone gets particularly busy after a TV showing of "That's Entertainment," and rang off the hook after "A Chorus Line" began its run.

"People are particularly attracted to tap dance because it's the most invitational of the dance forms. Watching the Bolshoi Ballet is an isolating experience, because while it's esoterically beautiful, it's not something an audience can do. But when someone watches 'Singing in the Rain,' the first thing they do is a little shuffle. There's no theory and no philosophy to tap dance - just sheer nutty madness and joy.

"It's therapeutic and escape-oriented, too," he said."There's a total abandon that comes from blocking out all thought processes and concentrating just on the steps. When you take 15 individual bodies and have them dance in a circle your class becomes a community - and if that's not dance thereapy, what is?"

Jeff said he began dancing "six months before I was born. My mother said she'd move near the radio, and I'd kick out a time step in perfect 6/4 rhythm." Like the dancer in "A Chorus Line" who finds "I Can Do That," Jeff learned the basics of tap from his sister. When she came home from dance class she'd show him a simple step and he'd turn it into a six-point turn.

At age six he was appearing in local musicals that needed child actors. At 14 he was teaching dance to neighborhood kids, and at 18 was teaching dance in a university.

He moved to Washington from New York 2 1/2 years ago when he fell in love with the city during a dance masters' convention.

Since he arrived, he has been teaching dance and theater arts at the Open University, a non-profit corporation that sponsors more than a hundred classes from How to Buy a Car to Vegetarian Cuisine.

Of all the classes he's taught, Jeff says, he enjoys teaching tap the most because his students get so excited when they find that they can dance.

"When I take someone with a sedentary, pedestrian way of life and teach them to tap it's like being a parent watching a child walk for the first time," he says. "The faces they make in the mirror are just adorable, and that's why I love it."