18 All?

When the score in a tennis game reaches a baffling 18-All, you know you're not at Wimbledon.

Boing. Boing. Boing.

When Tom Selleck, perched in courtside highchair, says to the audience, "You know, people's heads really do go back and forth. I thought that was just a film trick" -- you know you're not on a Hollywood film set.

Grrrrrrrr.

When the mohawked Mr. T, in tight Hawaiian shorts and glittery hightop sneakers with day-glo laces, is the "umpire" in the fourth match; when he warns he's "just calling it like I see it"; when he growls, "Double dribble!"; when he barks, "No more clashing of rackets"; when he muses, "Boy. God. Who woulda believed it? The White House. This is all right" . . . you know where you are.

You're at the White House for the second annual Nancy Reagan Drug Abuse Fund tennis tournament.

Or, as Mr. T put it, "If I was president, I would tell people to ree-laxxxx."

Behind the White House, enclosed by holly trees and greenery and approached by a narrow row of cool flagstones, the tennis court was transformed Saturday afternoon from a serene pocket of presidential privacy to a laughing, 250-person swarm of stars and spectators. Reeboks, pleated linen skirts, straw hats and polo shirts spread across the sunny bleachers. In the shade of a red-and-white tent, men in tuxedos presided over the refreshments: iced tea, lemonade, fruit, chips and little foil airplane packets of Eagle's honey-roasted cashews.

With WDVM's Glenn Brenner as master of ceremonies, the tournament was a four-hour parade of celebrities: tennis stars such as Stan Smith and the Amritraj brothers, Vijay and Ashok; television stars such as "Hill Street Blues' " Veronica Hamel and "Remington Steele's" Stephanie Zimbalist; Reagan Cabinet members such as Secretary of State George Shultz and Secretary of Energy John Herrington; and sports figures such as Julius Erving and Herschel Walker.

The tone for the afternoon was not imposed by the formal informality of a country club setting. Nor was it set by the substantial corporate patronage of Eagle Snacks, General Motors, Occidental Petroleum, Prince Manufacturing, Rapid-American, Reebok International, Stephens Inc. or United Technologies -- each of which, having donated $60,000 to the drug abuse fund, was allowed to invite 12 guests.

The tone was epitomized by Mr. T: "What do they mean when they spin that racket? . . . Why don't they just flip a coin? . . .Let's not do all this patty cake stuff. I know it's for charity, but let's make it interesting."

"Laughing is allowed at the White House," Brenner told the audience, though they needed no encouragement to chortle or cheer from the sidelines.

Mr. T, alternately keeping and not keeping track of the score, growled, "I run a tight ship." Hamel, partnered with James Baker, and playing against tennis neophyte Chuck Norris and former CIA director Richard Helms, quipped to the audience, "I wish you'd run a quieter one."

30-Love.

"What does this 'love' mean?" Mr. T demanded of Brenner. "Zero," explained Brenner. Mr. T shouted out "double fault" and urged the team of Baker and Hamel that they should "work on that other guy" (Helms), because Norris had only three weeks of tennis lessons under his black belt.

40-30.

"40-30, all right! All right! I'm gonna know this game by the end of the day . . . I know deuce. I know love. I'm learnin'," Mr. T said. "If you have any questions during the break," Brenner said to the audience, "Mr. T has a booth set up right over here" -- and he waived toward the refreshments area.

bat10 It was an afternoon of semi-lawless tennis (four points to a game, 20 minutes to a match, six matches to the event) and unrelenting one-liners. No second serves would be allowed "because of Gramm-Rudman," explained the "hey-just-joking" Brenner. And in desperate circumstances, serves could be done by proxy. So when it came time for Dorothy Hamill to serve, she let tennis pro Pam Shriver take a try. "I knew that I couldn't serve before I got here," Hamill laughed. Until invited to participate in the benefit tennis tournament, she had never played the game. "I'm humiliating myself," she giggled.

"I'll be glad when the First Family comes out," Mr. T said. "They're gonna straighten things up."

President and Mrs. Reagan arrived to catch the last and, by chance, most competitive match: George Shultz and Pam Shriver playing Dina Merrill and Stan Smith. "GO!" Shriver shouted to her partner; and Shultz, quiet and tenacious, charged after the lime green ball. "This is one of the few places you can yell at the secretary of state," Brenner quipped. In a tie-breaking game, Shultz and Shriver won.

The match over, Mrs. Reagan presented two checks of $50,000 each to the "Just Say No" club and the new Washington Fund for the Prevention of Substance Abuse. She thanked the corporate sponsors, whose contributions to the Nancy Reagan Drug Abuse Fund approached half a million dollars.

"This money will go a very long way in helping kids in their efforts to make a better life for themselves," she said and then invited the audience to "come up to the White House for some refreshments."

They did. And the postmatch afternoon, with a gentle breeze and a retreating sun, with plates full of roast beef and with cameras clicking at every and any photo opportunity, drew to a relaxed close on the South Portico of the White House.

The Reagans settled into some lawn chairs and chatted for an ample 45 minutes with a small tableful of celebrities, including Stefanie Powers, Merrill and Selleck. A few brave guests broke the inner circle and collected the Reagans' autographs. Shultz talked tennis shoes, not politics. Veronica Hamel, looking across the South Lawn, pointed out the Washington Monument and the Jefferson Memorial to Ashok Amritraj.