At 5-foot-6, Harold Solomon is still the Little Big Man of tennis, but he has grown up enormously in the past couple of years. His game has matured, and so has he.

Once a notorious berater of linesmen and fumbling ball boys, he is now impeccably behaved on the court.

At age 27, he is active in the affairs of the Association of Tennis Professionals, a firm and responsible voice on its board of directors.

He realizes, unlike so many spoiled modern pros, that he has an obligation to the public and the game that has made him a wealthy young man.

"I would like to help bring some integrity and some direction to tennis," he says, "because obviously what's best for the growth of the game is best for the players in the long run. We need some foresight to see what's going to be best for future generations of players."

Solomon -- who plays Bjorn Borg, a man he calls "the closest thing I've seen to the perfect tennis player," in the semifinals of the French Open here Friday -- is currently ranked No. 6 in the world.

He is working hard on his attacking game, intent on cracking the top five and aiming at bagging a major title. But his interests and concerns extend far beyond the confines of a tennis court.

He and his wife, Jan, a vivacious and thoughtful Texan, are heavily involved in the Hunger Project, a nonprofit, San Francisco-based organization whose goal is helping eliminate starvation in the world by the end of the century.

Many people are skeptical of the organization, which was founded by Werner Erhard, the creator of the est consciousness-raising organization. The Solomons, however, are convinced that the Hunger Project is on the right track, and are committed to raising new members and money for it.

"The National Academy of Sciences came out in a report and said that, for the first time in history, we have the food, the money and the resources to end starvation within a lifetime," Solomon says. "The only thing that's lacking is the will to get the job done. We're trying to create the will to see starvation ended in the world."

The Solomons operate booths at many tennis tournaments, enrolling people in the Hunger Project and soliciting contributions. They have signed up approximately 5,000 so far.

At home in Pompano Beach, Fla., when Solomon is not playing tournaments, they do lectures and make presentations to high school students, stressing the magnitude of starvation and hunger-related diseases in the world, explaining ways that people can help get food that is currently wasted to the 15 million people who starve every year.

Solomon has decided to donate a portion of the prize money he wins at tournaments this summer, probably beginning with the Washington Star International in July, to the Hunger Project. He wants to enlist businesses and corporations in each city he plays to make matching contributions, and to present the funds during the U.S. Open in New York in September, where he hopes to generate international publicity for the charitable project.

It was his growing interest in the problem of world hunger, Solomon says, that helped him rededicate himself to tennis a year ago, and embark with a new coach on a comprehensive program to improve his game and his ranking.

"It kind of gave me a little more impetus to go ahead and want to do it, so that I would have more impact, and be more recognizable to the public, when I talked about the Hunger Project and tried to get things done for it," he says. "It's a lot easier to go out and kill yourself practicing if you have a higher purpose than just getting better. If you feel you're making a contribution to society, its easier to get up in the morning and work than if you're just doing it for yourself."

Solomon says his moment of recognition came during a six-day est course he and Jan took last June. "I saw that I had kind of just been stagnating, ranked around ninth, 10th or 11th in the world, but not making any progress in my game, just doing the same things instead of trying to improve."

He went to Paul Cohen, who coaches a number of nationally ranked juniors in Los Angeles and who had worked with Solomon's teen-age sister, Shelley, and together they analyzed his game. The verdict: he needed to be more aggressive, to build up his serve and volley to complement his solid backcourt game and passing shots.

"We sat down and decided that I'm not getting any younger, and in order for me to continue progressing, I had to be able to come up with an ace or a big serve occasionally, and to go in and knock off a volley," Solomon says."I had to be able to win points and matches quicker than I used to.

"The idea is to transfer some of the pressure to the opponent instead of me having to come up with the passing shot all the time, especially on the big points. I needed to put pressure on the other guy, to get him guessing whether I was going to stay back or go to net on a big point. It's kind of unsettling to the guys who have played me for years to see me coming in.

"I just took two months last year and worked on volleys, volleys, volleys. I used to be very uncomfortable at net, but now I feel at home there. I've always had good approach shots, but I never used them. Most of the time, I didn't follow them in. Now I go on every short ball. I try to be the aggressor all the time."

Solomon thinks he is a much more complete player than he was in 1976, when he became the first American in 21 years to reach the final of the French Open, lost to Adriano Panatta.

"I serve and volley a lot better now. I hit the ball a lot harder. I'm able to hurt guys a lot more," he says. "I used to wait for people to make mistakes. Now I go after the shots and try to force the mistakes."

When he started on the international circuit, Solomon was the king of the "moonball" -- looping, topspin ground strokes that he hit in endless profusion. "He was grit and guts personified. He won on patience and stamina.

He took pride in being in great shape, a fighter willing to stay on court all afternoon to wear a foe down and grind him into submission. The ultimate victory was when he "pretzeled" an opponent -- left him twisted in cramps, unable to finish a match.

"I really didn't have the equipment to just knock guys off the court and get the match over with fast, so I had to rely on those other things -- working hard, staying out there, being in good shape. Now I use the equipment I have to win quickly and conserve some energy for the next round. I think I'm in better shape than ever. And if the new attack doesn't work, I always have my old style as a backup," he says.

Solomon gives full credit for his improvement to Cohen, who has worked with him intensively for 12 months, and this year is traveling to a number of tournaments with him. Cohen was in Las Vegas six weeks ago when Solomon got to the final, losing to Borg. He was in Hamburg last month when his pupil won the German Open in a five-set-final over Guillermo Vilas. He was here when Solomon beat Vilas in the quarterfinals. He will be at Wimbledon, where Solomon will play later this month for the first time since 1977.

Most of the top players who have taken on coaches, a growing trend in pro tennis the past six years, have gone to former top players. The theory was that only a fellow who has experienced the pressure of competition can appreciate it. Solomon's choice of Cohen is, he says, a new twist.

"Just because you're a good player doesn't mean you're a good teacher, that you can convey what needs to be conveyed," he says. "Paul is a student of the game. He knows a lot about it. He knows what works for me, and works systematically on it.

"It's been a problem for him because some people look at him and say you have to have been a great player to coach. It's tough, because he feels that he has to justify himself a lot of times. I don't feel that need at all. I just look at the evidence: I was No. 11 when I went to him, I'm No. 6 now, and my game has improved steadily."

That, too, is a very mature attitude, a bit more of the ample proof that little Harold Solomon, from Silver Spring, Md., has, like his game, grown up.