Exploration of the possibilities is still in its earliest stages, but there is a chance that the Washington Star International tennis championships may be played in late August instead of July next year, and on hard courts rather than clay.

The 10th annual Star tournament ended Sunday with a record cumulative attendance of 70.700. despi te one session fewer than a year ago. Tournament cochairman John Harris confirmed yesterday that consideration will be given to a trade of dates with Boston's U.S. Professional Championships, now played the last week in August, immediately before the U.S. Open.

The U.S. Pro is having difficulty attracting a good field because it is played on clay the week before the U.S. Open, to be contested on hard courts for the first time at its new site in Flushing Meadow, N.Y. Most players like to have at least a week or two of play on the same surface before a major championship.

The Association of Tennis Professionals, which copromotes the U.S. Pro with the host Longwood Cricket Club in suburban Brookline, Mass., urged the installation of hard courts for the tournament this year, but the Longwood Board of Governors has adamantly opposed any change of surface.

The club seems to favor a shift of dates next year to the early part of the U.S. summer tournament schedule, which will continue to be on clay. An exchange of dates with Washington, and installation of hard courts at the Washington Tennis Stadium, 16th and Kennedy streets NW, has been suggested.

"It's a subject that will be discussed among U.S. tournament directors. There may be some shuffling of the summer schedule," Harris said yesterdy. "It's too early to tell what will happen. But if Boston wants to change its dates, we might be interested - if we could get permission to change the surface at 16th and Kennedy."

The tennis facility in Rock Creek Park, where the Star tournament has been played since its inception in 1969, is owned by the National Park Service and operated by Government Services Inc.

There are presently 17 Har-Tru (artificial clay) and five Laykold (hard (hard surface) courts at 16th and Kennedy. Hard courts are easier and less costly to maintain than Har-Tru, but less popular with the recreational players who patronize the public facility throughout the outdoor tennis season.

The Star tournament might attract a stronger field the week before the U.S. Open because there are fewer competing tournaments that week and more players in the United States. The current dates, two weeks after Wimbledon, conflict with several European tournaments and Davis Cup.

However, there is an increasing tendency for the best players to take the week off before major tournaments. Bjorn Borg, Jimmy Connors (who recaptured the Star title he first won in 1976), and defending champion Guillermo Vilas are all sitting out the week before this year's U.S. Open.

Donald Dell, Harris' cochairman, said yesterday he was discinlined to change the Star dates "because I feel we've built a tradition here as the first major tournament in America after Wimbledon."