Bud Schultz was lying in the Wimbledon locker room trying to keep his hands from jumping to his throat and the perspiration from pouring down his face harder than the rain outside.

In a futile effort to distract himself from his case of nerves, Schultz glanced at the television monitor, which showed John McEnroe and Peter McNamara leaving Centre Court in a downpour. They walked out of view of the camera and then came through the locker room door, strolling into Schultz's life just like that.

"I was a wreck," Schultz said. "I was so nervous, everyone else was telling me to get out of there. I'm watching the TV, and it was the oddest thing. They walked out of the TV and into the room. I broke out in a cold sweat. That was when it all became real for the first time."

For a throat-contracting situation, however, Schultz probably will have it worse Saturday. The 26-year-old player from Boston, who is in his first full year on the tour, will face McEnroe in the third round of the U.S. Open on the Stadium Court at the National Tennis Center. McEnroe was a 6-0, 7-6 (7-3), 6-1 victor over Martin Wostenholme today. On a distant court, Schultz defeated Richard Matuszewski, 6-3, 6-4, 7-6 (9-7).

Schultz, who is 6 feet 4 and formerly played college basketball, has made a sudden and intriguing entrance into professional tennis. His only previous claim to tennis fame was a runner-up title in the 1981 NCAA Division III finals while attending Bates College in Maine.

Schultz is an odd sort of ingenue. On that rainy day at Wimbledon, he defeated Aaron Krickstein in their first-round match. Schultz made the quarterfinals in Toronto earlier this year. The rest of his season has been a series of first- and second-round losses, but many want to know about the aging newcomer who threw away a master's degree for a shot at the tour.

Before this year, Schultz spent most of his time playing the New England circuit when he wasn't serving as an assistant tennis coach at Boston University, where he also pursued a master's in psychology. But he tired of graduate-student life, and tennis friends encouraged him to try his hand at the tour.

He was ranked No. 1 in New England last year and won a small tournament in Pittsfield, Mass., where he collected a grand total of $1,000, before hitting the ATP circuit in the middle of last year. His first match victory came in Memphis in January, when he won a first-round meeting with Victor Pecci.

On paper, McEnroe shouldn't have much trouble with Schultz. They met three weeks ago in the Volvo International tournament in Stratton, Vt., McEnroe winning, 6-3, 6-3. After his match today, McEnroe viewed Schultz's serve-and-volley game as an important, although not particularly threatening, tuneup for a potential meeting with Boris Becker in the quarters.

Schultz may have a surprise for McEnroe.

"I learned a couple of things from the match in Stratton," Schultz said. "I learned not to try to overplay him; he has a tendency to make you feel you have to do that. And I learned to stand up for my own rights. I may not win a single game against him, but hopefully this time I'll be able to relax and play him better. And there's always a chance I can win. Stranger things have happened."