George Mason University will break ground for a 5,200-seat fieldhouse on its Fairfax campus May 6, so . . . Coach Joe Harrington breaks new recruiting ground for the Patriot basketball team: check Flint Hill Academy today for the word that all-Met Carlos Yates will join GMU's 1981-82 squad.

Yates, 6 feet 5 and physical, shot 60 percent and scored 24.5 points a game for Mike Pepper's old school the past season.Indiana and Purdue courted him. But Harrington's got him, possibly to play power guard. Will he be ready, right off, to face prespective opening-week GMU opponents, Virginia and Maryland? That's right; Cavs and Terps, if expectations materialize . . .

They come and they go. Dominique Wilkins, the 6-foot-8 Georgia forward just two years removed from Capital Classic high school all-star brilliance, and his folks had a visit from Jack McCloskey on the eve of the Detroit Piston executive's confab with Ralph Sampson -- and the SEC supersophomore refused a guaranteed four-year, $1.28-million NBA contract.

Still, Georgians already sweating out freshman footballer Herschel Walker's decision on a pro offer can't relax. Wilkins said he told McCloskey "that was a good contract offer, but that wasn't enough for me"; added that he expects the Pistons to better the $320,000 a year bid, and, when asked what he would consider enough, replied: "I think about $375,000 a year. In that range."

Wilkins also was standing by for a call from the New Jersey Nets . . .

In Chicago, De Paul's all-America junior Mark Aguirre has indicated he will tell probably Friday whether he is available to the NBA.

A De Paul athletic official meanwhile assured, "Mark has gone to all of his classes and has been taking makeup exams."

Aquirre promised to tell Coach Ray Meyer of his decision before making it public. Meantime, there is Aguirre's Chicago buddy, Isiah Thomas, the sophomore dynamo of Indiana's NCAA champions. And another De Paul official said, "Mark is waiting to see what Isiah does. It could mean a lot in terms of a contract if he, Thomas and Sampson all turn pro before the end of their (college) careers" . . .

Tragedy in track and field: hammer thrower John Tucker of Chicago, one of the Midwest's best, fatally injured when the 16-pound implement -- a metal ball with flexible wire handle -- got away from a competitor and hit him in the head. Tucker was waiting in a "safe area," behind a fence and 20-30 yards to the right of the thrower warming up for the Illini Classic meet . . .

More recruiting: Holy Cross girls basketball all-Met Jackie Isreal opts for schoolmate Karen Elsner's choice: U. of Richmond . . . Karl Racine, St. John's guard eyed by AU and GW, likely to declare shortly for Penn . . .

Doings: "Black Baseball: Life in the Negro Leagues," collection showing through May 15 at Smithsonian's Nationanal Museum of American History. Some of the players who donated artifacts will visit the museum Friday, 1:30, for a special presentation program . . . At Green Spring Racquet Club, Baltimore, 7:30 p.m. Thursday and Friday, 1 and 7:30 Saturday, finals at 1 Sunday: $33,000,000 Legends of Tennis tournament. Laver, Rosewall, Emerson et al. in third stop of 10-city tour.