If you think only young Washingtonians such as Zbigniew Brzezinski have a lock on the disco circuit, consider California's junior senator, Republican S. I. Hayakawa. At 73 years of age, Hayakawa cuts a mean figure on the disco floor one -- sometimes two -- nights a week at such places as The Polo Club. When reached at home recently and asked the secret of his stamina, he had just finished cutting down a tree in the yard of his Capitol Hill home. Really.

The Hayakawa disco diet is fish, vegetble and chicken -- very little red meat, and no bread or potatoes. Three squares a day. Rise at 7:30 or 8:30 in the morning. At home he tap dances. No jogging -- "I'm too lazy," he says. Two or three times a year he goes scuba diving in California, where his wife lives most of the year caring for their son, who is mentally retarded, and working on two horticulture magazines. The senator often takes to the dance floor with friends and office staff. Preferred drink when boogying: a scotch and soda or two, no particular brand. "I do disco, after a fashion," Hayakawa says. "I learned to waltz and foxtrot in college in the '20. Its not that I dance well, but I dance with a lot of self-confidence."