The tennis-playing boom may or may not be subsiding, but the tennis-watching mania pointed up by those teeming Wimbledon crowds lives:

Washington Tennis Stadium, 16th and Kennedy Streets' counterpart to the All England Club's Centre Court, is sold out for the July 23 finals of the $175,000 Washington Star International tournament.

Codirector John Harris' announcement marks the earliest date in the event's 10-year history that all 5,800 seats have been claimed for the dlimax of the action that commences Saturday for a nine-day run.

Arthur Ashe, the 1973 champion, is entered in the 64-man singles draw (sponsors will determine pairings via a second annual media draw party at the Shoreham Americana tomorrow evening) so becomes the only player to have competed in all 10 Star Internationals. And in doubles, Ashe will team with Bob Hewitt, the graybeard half of the 1978 Wimbledon champion team of Hewitt and Frew McMillan With Jimmy Connors entered, about all that will be missing besides Bjorn Borg's shaven-off beard is Bjorn Borg.

But what the heck, you can't have everything. Or anything, in the case of the phantom of RFK Stadium, doing (no) business as the Freedom Baseball League.

The big announcement of Friday that professional baseball was back with action starting Friday, Sunday and Monday fizzled because the Freedom man, Art Peterson, failed to post the hefty deposit (running to four digits per date) to cover stadium services over and above the rental. Teams had taken the field for pregame practice and "fewer than 100" paid admissions were in the stands the first day, when the cancellation was decreed. Stadium Manager Bob Sigholtz said last night he had talked with the would-be tenants again Saturday night, about possibly opening play Wednesday - "and haven't seen or heard from them since."

Now it's Wednesday. Peterson (who had the Seattle franchise in the Pacific Coast League and received something like $60,000 indemnification when the American League returned with the Mariners) and company took out two telephone numbers last week to supply ticket information about the four-team (anonymous-talent) league's Washington schedule. Nobody answered our rings the past two days. Darn . .