The National Park Service is considering several major changes at its more than 30 tennis courts in Rock Creek Park, including construction of a year-round indoor tennis complex and lighting outdoor courts at 16th and Kennedy streets near Carter Barron Theater.

It also is considering permanently closing all six clay courts at Pierce Mill, popular with area residents for more than 50 years.

The nonprofit Washington Area Tennis Patrons Foundation, a sponsor of several major tennis tournaments here and tennis programs for thousands of area children, is interested in making a major contribution both to build an indoor tennis complex at 16th and Kennedy and to light additional outdoor courts, according to foundation president John Harris.

It already has spent more than $200,000 on improvements there since 1969, including grandstands, lights on two center courts and lockers and rest rooms. The outdoor courts are used primarily during the annual Star International Tournament in July.

The foundation hopes either the Park Service or Government Services Inc. (GSI), the nonprofit group that operates most tennis courts, marinas and food concessions in federal parks here, will contribute part of the cost if there is interest in the idea. It is expected to cost more than $500,000.

"We've not been asked to look at such a thing," GSI vice president Walter Williams said last week. "Basically we're a tenant and are responsive to what the Park Service wants, and we had told them at one point that we'd be interested in doing a feasibility study of it . . . but our first interest is in doing something economically sound."

With 22 courts at 16th and Kennedy, the Park Service already has the lartest public tennis complex and the largest number of clay courts (17) in the Washington area. At Hains Point it has the second largest, with 18 courts, including 10 clay. Both are operated on a fee basis by GSI, but there are many free courts on federal parkland here, including four at Montrose Park in Georgetown and even two on the Ellipse.

The possible closing of all six scenic clay courts on Park Road near Pierce Mill, built in 1925 and surrounded by tall trees, was revealed publicly for the first time last week at a Park Service planning workshop held to discuss "alternatives" for the park's many tennis courts.

The meeting at Rock Creek Nature Center was attended by less than two dozen of the thousands of area tennis players who regularly use the Rock Creek courts. They criticized the Park Service for inadequately advertising the meeting and for allegedly having a "secret agenda," as one person called the previously undisclosed Park Service proposal to close the Pierce Mill courts.

Most said they had come because of rumors the Park Service was considering paving over the 17 clay courts at 16th and Kennedy streets, a proposal made earlier this year by the tennis foundation but later dropped. The audience was unanimously opposed to paving any soft courts at 16th and Kennedy or eliminating any courts at Pierce Mill, and were strongly in favor of improving and expanding the 16th Street tennis complex.

Iris Lipkowitz, who said she first learned to play tennis at 16th and Kennedy, called it "absolutely outrageous" that the Park Service should even be considering elimination of tennis courts when the demand for courts in Washington is still growing.

Rock Creek Park Superintendent Jim Redmond said in answer to questions that the elimination of the Pierce Mill courts was "one of my personal feelings . . . because they're in a forest area, a natural area, that shouldn't have been developed in the first place . . . and I don't think the Park Road (Pierce Mill) tennis courts are that important."

However, Redmond said he hadn't yet discussed closing the Pierce Mill courts with Park Service planners and that no action would be taken without a public hearing.

GSI's Williams, contacted after the meeting, said the Park Service "recently asked if we were opposed to closing" the Pierce Mill courts "and we said no, certainly not if they were replaced by five or six additional courts" elsewhere such as at 16th and Kennedy.

Redmond told the meeting GSI was losing money operating the Pierce Mill courts and barely covering its costs at both 16th and Kennedy and Hains Point. Williams confirmed that, but said "tennis things normally only break even," although he said that before the tennis boom of the last seven years most of the courts regularly lost money.

GSI recently raised its court fees, although its indoor prices - for the five hard courts under a bubble tent at Hains Point - apparently are still the lowest in the Washington area. Clay courts are $4.75 an hour and hard courts $2.60 during prime time (weekends and weekdays after 4 p.m.) and $2.75 and $1.65 respectively during non-prime time or "off time." Indoor courts range from $7-$13 an hour but no membership fee is charged.

Williams said that Pierce Mill actually is the most heavily used of GSI's tennis complexes, with courts there in use 90 percent of prime time. But he said that is probably because of the unique arrangement there that every year allows tennis players to buy season tickets reserving a court regularly at a particular hour.

Over the whole spring-to-fall season in prime time, about 70 percent of the 16th and Kennedy courts are in use and about 55-65 percent of the Hains Point courts, Williams said, although construction of Metro beside the tennis courts has noticeably affected use of the courts.

Off-time use can range from 25 percent at the GSI courts to 55 percent, depending on the month, with little demand in May and peak demand in July.