TWENTY YEARS AGO Althea Gibson was the queen of the tennis court. As she won the premiere world tennis event, Wimbledon, in 1957 and 1958, followed by a sweep of the American tennis classic at Forest Hills, her breakthroughs in the all-white world of tennis earned her the title, "the Jackie Robinson of tennis."

And, just as the world had loved the sagas of the other "firsts," Jack Johnson and Robinson, they idolized the first black tennis star. At Wimbledon, the contrast was dramatic: the tall, gangly, still rough around the edges 29-year-old from Harlem accepting her trophy, curtseying timidly and fighting the tears, from the still new-to-be-throne symbol of gentility, Queen Elizabeth II of England.

In the intervening years Gibson, who will be 50 in August, has by no means forgotten the glories of Wimbledon, but right now she is concentrating on another game - politics.

She is running for the New Jersey State Senate on a ticket headed by Rep. James Florio (D-N.J.) and their first hurdle is a primary Tuesday.

"I have always wanted to do things that were beneficial to the public. But politics, I guess I was mildly surprised at my decision," said Gibson. "I thought about what I had read about crooked politicians, the kind not concerned with people, but then I finally thought, maybe this way my chance to do something for a number of people." A few months ago, because of frustrations with the bureaucracy, Gibson resigned her job as the New Jersey state athletic commissioner for boxing and wrestling, a part-time, $7,000 a year post she held for 14 months.

On the campaign trail, through the rounds of champagne breakfasts in East Orange, where she lives, through the walking tours of Hackensack and other Jersey towns, Gibson is a good drawing card. "People recognized me. They haven't forgottten and I feel good," said Gibson, her voice even deeper than usual because of the speaking strains of the campaign.

Like many stars, especially the sports breed, Althea Gibson has never totally disappeared from the scene. During the years of her Wimbledon and Forest Hills titles, she was named the Associated Press Woman Athlete of the Year. In 1960, after winning the world professional tennis tournament, Gibson retired, only to join the women's professional golf circuit in 1963.

"I had won the major titles. There were no more challenges in tennis," said Gibson. At the time tennis trophies were simply statues and gold plates, without any money attached, and Gibson needed to learn a living. "I guess I was way ahead of the times. Now tennis is very profitable. But I don't cry over spilled milk. I feel I accomplished a great deal," she said.

Yet she tried other things. Evan before she retired, she made one record album and appeared on "The Ed Sullivan Show." Later she made a movie with John Wayne and William Holden, titled "Horse Soldiers," wrote her autobiography and traveled for one season with the Harlem Globetrotters. In more recent years she has been a teaching tennis pro at various clubs.

As expected she has more than a passing interest in the current hoopla over physical fitness. "I think it's great. Physically I am very prepared for the rigors of campaigning. I play tennis indoors all winter and then play golf in the summer. No, I'm not into jogging, but if I feel a little out of shape I play tennis and run on the indoor track at the Y," said Gibson.

And politics and sports have their parallels for the tennis great of the 1950s. "I have to look back on my competitive tennis days. I go at politics vigorously, I go out to win, not to be just a participant."