Saturday afternoon, in view of the Lincoln Memorial. A CIA man is doing everything he can to stop the Soviet aggressor. The two alternately advance and retreat, guarding against feint or folly. Each looks for subtle clues to the other's next move, until the ball escapes the dirt court, heading east on Ohio Drive.

No one will say for the record whether the superpowers have actually squared off across a volleyball net; but a United Nations of athletes assembles each weekend on the four courts between the Memorial and the Kennedy Center. Showoff spikers and social players, diplomats, military men and bureaucrats set up and slam as long as there's daylight.

Anyone can break into the action, especially before peak season. "In another month, they'll be lined up waiting to play," says Gwen Casey, one of a minority of female regulars.

For nearly a dozen years, a core group of about 30 not terribly proficient but dedicated players has been meeting here weekly, whenever the temperature climbs above 45 degrees and with time-outs for thunderstorms. An international mix, they reflect volleyball's popularity around the world. In 70 nations, more kids grow up volleying than playing any other sport, except soccer and football.

Before entering the fray, be advised that the regulars snub "jungleball" players who have more enthusiasm than skill. Rank beginners are relegated to one court.

Also know they stick to USVBA ruses: six people on a team, three hits on a side before the ball must be sent over the net, courts 30 feet by 30, nets five feet off the ground and a 15-point game. A range of stunning to adequate serves -- underhand, overhand or sidearm -- are acceptable. Most games last roughly 20 minutes.

The Mall's pickup games draw "a pretty intellectual group," observes Jim McKay, himself a Navy research physicist. "We have lots of doctors, lawyers, an engineer and CIA guys." The Brazilia nand Russian embassies are known to have good teams, and at times they take over the courts, beating all comers.

"When it gets warmer there'll be lots of Samoans out here. And more women, too," says Jerry Bolton of Alaska, another regular.

Lots of Washington types, too. Economists from Brookings play Hill staffers, neither side demonstrating the form nor intensity of California beach players. Leagues and intraoffice matches sometimes hog the courts for more organized volleyball competition.

Devotees remember when they were limited to two courts, in what's now super-land-scaped Constitution Gardens. Now that they've got four courts and more than enough people to keep them busy, they've got another demand.

"We want the portable bathroom back," says Bolton. (The National Park Service replies that it doesn't have the money to rent one there this year, and points instead to the Memorial's facilities.)

Permits for the courts are available through the D.C. Department of Recreation. According to staffer Patricia Mason, there aren't enough to go around from May through September. Permits -- usually snapped up by office groups for weekday and early-evening hours -- may be obtained in person or by writing the department at 3149 16th Street NW. (Call 673-7646). They're free, must be renewed monthly and have a two-hour playing limit.