John McEnroe had the good fortune to draw, then defeat easily, the 437th-ranked player in the world in the first round of this week's Volvo International in Stratton, Vt. Unfortunately for family harmony, that person was his brother, Patrick McEnroe.

Although siblings meet infrequently on the professional tennis tour, where only a handful play, such situations are not uncommon in the amateur ranks.

In next week's American Tennis Association National championship at the Rock Creek Park courts, brothers Lange and Julian Johnson are entered in the open singles division. Lange, 23, has a three-two edge in tournament competition over 27-year-old Julian.

"We've played each other many times but only five times in tournaments," said Lange Johnson, the 14th-seeded player in next week's tournament. "I've won the last two times, but we're still very, very close."

What's the sure-fire strategy for playing a family member? "You just try to block out the fact that it's your brother on the other side of the net," Lange Johnson said. "Naturally you're a little more relaxed because one of the people you want to win is going to, but it's still hard."

Lange Johnson's grandfather, Robert Johnson, who lives in Lynchburg, Va., used to coach Althea Gibson, the first black woman to win the U.S. Open and Wimbledon. His father, Robert Jr., has played competitive tennis most of his life and will play here next week in the ATA 55-over division.

Robert Johnson used to take his son Lange to the pro tournaments at Rock Creek stadium. "I used to watch the lefties, Orantes, Laver, then try to apply what I learned by watching them." By age 13, Lange was good enough to beat his dad.

His high school tenure reads like a travelogue: from Potomac to boarding school in Simsbury, Conn., to Wilson High School in the District to Bradenton, Fla., home of the fabled Nick Bollitieri Tennis Academy.

The last time the ATA championships were held in Washington (1972), Lange Johnson won the 12-and-under division. He did not have to play his brother then.

"I hope I don't have to play Julian in this tournament," he said. "But if I do, I hope it's in the finals."

The tournament begins Monday at 9 a.m. Adults play at the Rock Creek courts at 16th and Kennedy Streets NW, with the men's and women's semifinals Friday at 10:30 a.m. and the finals on Saturday; women at noon, men at 1.

Junior matches will be held at the East Potomac courts at Hains Point from Monday through Saturday.

Today from noon to 5 there will be celebrity matches at Rock Creek, featuring Mayor Marion Barry, Capital Centre owner Abe Pollin, media personalities Glenn Brenner and Renee Pouissant, and former Washington Bullets forward Bobby Dandridge.