On a flat piece of ground in Rock Creek Park, across the street from a set of swings and across another street from a softball field, a couple of bulldozers are eating away at the orange earth as part of a grand plan that signals a new era for tennis in Washington.

A new tennis center is being built, very slowly. This is a $6 million to $7 million project made necessary by the changing times -- and surfaces -- of professional tennis. It is not without controversy; although ground has been broken, it has been broken gingerly, because all the plans for the facility have not yet been approved.

This is a change not only for big-time tennis, but for a neighborhood full of tennis players. It is coming about on public, National Park Service land and it is being done with private funds. It has not been easy.

Sandra Alley, a spokeswoman for the park service, which administers the facility at 16th and Kennedy Streets NW, said construction work has begun only on 11 additional hard-surface courts so that this year's Sovran Bank/D.C. National Tennis Classic can be played. However, Alley said, final approval by the park service for the entire project, including the new stadium, has not been issued.

If the project is not approved, the 11 new courts under construction could be removed, Alley said.

The problem, according to a park service source, is whether the project meets all criteria established by the park service, National Capital Planning Commission and Fine Arts Commission. The same source noted that the primary concern among some planners is whether the entire facility might be too large for the area.

"It will take a couple of years for people to understand that this is not bad," said Henry Brehm, director of the Sovran Bank/D.C. National Tennis Classic. "Right now, they hear about a big tennis center and say, 'Oh, God,' because they're thinking in terms of another RFK Stadium."

When construction on the facility is completed in a year or so, and if all goes as planned, the new tennis center will seat 7,500, where 5,000 now can sit; it will have more room for players; it will have more courts for public use than the facility has at present; it likely will draw more name players to the city to play in its summer tournament. Delayed Reaction

What is happening at the Rock Creek Tennis Stadium, simply stated, is a delayed reaction to the U.S. Open's switch from a soft to hard surface in 1978. In tennis-speak, the change here in Washington will be from Har Tru, the traditional synthetic clay surface, to DecoTurf II, the same hard surface used at the U.S. Open each September.

By July 27, when the D.C. tournament begins, Washington's men's professional tennis tournament will have been transformed to a state-of-the-art event. And, if the plans are approved, at least part of the center itself will be built by 1988; by 1989, it will be finished.

Last winter, at a fundraising exhibition at George Washington University's Smith Center, top-ranked Ivan Lendl told the audience he planned to play in the D.C. tournament this year for the first time since 1982, and probably would play in it in future years, for one reason: it was changing to a hard surface.

Since 1978, and especially in the past few years, the tournament had faced a dilemma. It held a prime spot on the calendar, between Wimbledon and the U.S. Open, but many of the big-name players did not want to come here. They were looking for a hard surface on which to prepare for the Open. Clay was not it.

"We were stuck," said Brehm. "There was no reason for any players to play clay with the U.S. Open coming up. If we didn't change, I think the tournament would have eventually just gone away."

Of the five heretofore traditional clay-court tournaments in the United States between the French Open and U.S. Open, only one will be played this season on clay, the tournament in Boston, July 6-12. The other four, including Washington, have either moved to another time of year or changed to a hard-court facility on the same or a different site.

A year ago, the organizers announced their intentions to switch rather than fight a trend. Since then, Brehm said, nine sets of drawings have crossed his desk, and the latest might not be the last. But, for all the headaches to organizers, promoters, Rock Creek Park personnel and local residents, the change has given the tournament what is considered to be its best field in years.

Lendl is scheduled to play, and so are Jimmy Connors, Aaron Krickstein and Yannick Noah, among others. The previous few years, the tournament had struggled to entice big-name players onto its clay. "We were getting butchered in the media," said Brehm. "We were being called a no-name tournament. People were asking, 'Where are the big players?' "

But even with big names, the tournament takes up just one week a year. The rest of the time, locals shell out a maximum of $7.50 per court per hour or a minimum of $3.25 per court per hour (depending on the surface and the time of day) to use the courts. The first plans for the new facility called for the elimination of some clay courts, to be made over into hard courts. This didn't sit well with some, so those plans were shelved, according to the planners, including the Washington Area Tennis Patrons, a nonprofit, charitable organization that is the chief beneficiary of the tournament, and ProServ, the Washington-based sports management corporation that manages and promotes the tournament and is headed by Donald Dell, one of the most powerful individuals in tennis. Public Concerns

"I guess a pulse was not taken," said Georgia Ellard, superintendent of Rock Creek Park. "When opinions were expressed, the tennis patrons were sensitive to the needs and feelings of those who use the facility."

Earlier this spring, two public meetings were held for residents to discuss the plans, Ellard said. What came out of those meetings was the plan on the table. The facility now has five hard-surface courts and 15 soft-surface courts for public use. (Two more soft courts are in the stadium.)

If the present plan is approved, the center, when completed, will have 15 clay courts and 10 hard courts, all open to the public. There will be a hard court in the main stadium.

The five new DecoTurf II (hard) courts are being built on a softball field used for league play. A new softball field is being created on a vacant area across Morrow Street at the patrons' expense, Ellard said, so play will not be interrupted.

"I consider it a pretty good compromise," Ellard said.

Although plans for such things as a players lounge, locker rooms and an interview area still have to be finalized, the basic design of the tennis stadium generally is set. The court will be sunk 10 feet into the ground so that the stands do not rise too high off the ground, said Jonathan Sloat, tennis center coordinator.

"We anticipate {the stands} will be four or five feet higher, but that's about it," Sloat said. "There is no rule how high the stands can be, but we want it to be an attractive place. The higher it is, the more austere it becomes. We are aware of the surroundings and want to keep the center looking like it belongs in a park."

Sloat said about $1.75 million already has been raised for the construction and redesign of the facility from contributions and pledges from private sources. Brehm said the rest of the money is expected to come from private donations and contributions; the leasing of 24, $100,000 court-level suite boxes; the purchase of 1,000 box seats, and the naming of individual courts in honor of donors who contribute $50,000.

Organizers hope all this eventually will mean more money for the patrons, a 31-year-old organization that sponsors tennis programs for local children, for handicapped children and for seniors, among others.

The patrons, with a budget of $225,000 to $250,000 a year, receive about $100,000 annually from tournament proceeds, said Sloat, a past president of the patrons. He said the group will receive the first $50,000 from the tournament's net proceeds, then split the rest, 50-50, with ProServ.

The park service will continue to run the facility, according to Alley.

"With better facilities, we will provide more money for the tennis patrons and a better tournament for Washington," Sloat said. "We think these changes are all for the better."