AS WASHINGTON'S intrepid tennis fans have found out this week, thunderstorms haven't been the only thing blocking out the stars at Rock Creek Tennis Stadium, where the annual D.C. National Bank Classic is in full swing. Some of the biggest stars never came to play; and others dropped out of sight early on. But here, as all around the world of the men's professional tour, serious questions are being raised about the effects of money on the game: on who shows up to play, and how that play goes. Pro tennis is, of course, private industry. But so is professional wrestling, where the fans accept certain arrangements that accent exhibition over straight competition.

Tennis fans, however, don't know enough about what arrangements might be altering the character of what they're watching, as an expos,e by newspaperman Michael Mewshaw points out. In a critique of his report, Arthur Ashe writes in today's Sports section that guarantees, or appearance fees, are in fact rampant, and do "threaten to unravel the already fragile credibility of the men's circuit." Mr. Ashe also says he believes--but cannot prove--that umpires are "instructed" to or do apply double standards in enforcing rules on top players and lesser players. And there are questions, too, about how seriously players take doubles matches.

But as Mr. Ashe also notes, serious efforts are being made to enforce standards and rules. The Men's International Professional Tennis Council did suspend Guillermo Vilas for allegedly accepting $100,000 to appear in a tournament in Rotterdam. If the circuit's smaller (lower-purse) tournaments-- and the $200,000 D.C. Classic is one--are to compete at all, guarantees make it tough to impossible.

If the tennis industry wants its stars spread around and the competition serious, other suggestions may deserve consideration. John Harris, cochairman of the D.C. Classic, would like to see the Pro Council actually tell the top players to play certain tournaments. Some officials have suggested that players who reach semifinals be given bonuses as incentives to show up and play hard in tournaments that they might otherwise pass up.

In Washington, of course, the council might consider either incentives for the weather people to adjust the climate or limiting contestants to mad dogs and Englishmen. Truth in labeling and packaging is all anybody can ask.