The trouble with Ralph Sampson, the youngsters found out yesterday, was that they had to tilt their heads at an unnatural angle just to talk to him.

Few of the 120 hopefuls at the Northern Virginia Basketball Camp, where they will shoot baskets all week at the W.T. Woodson High School gym, stood taller than 5 feet. Sampson, the Virginia center on hand to talk about rebounding and boxing out, was an attraction as much for his height -- 7-foot-4 -- as for his court technique.

"I was here last year, when Ralph came then," said Steve Skinner, 12. "He was a giant then. I think he's grown more."

Sampson, who attended four basketball camps the summer between his junior and senior high school years in Harrisonburg, Va., knew what the youngsters wanted to see.

He wore a United States team practice jersey that he had brought back from the Pan American Games in 1979, and inpressed them with moves that aren't found in college games. He performed, by request, both backward and full-twisting dunks.

"Oh, Ralph just did his moves," said Byron Schafer, 7.

One of them involved Sampson's contention that "anyone can dunk." Schafer, at 4-foot-o the smallest player, dribbled to Sampson, who lifted him to basket height so Schafer could finish off the slam-dunk of his young life.

"Byron's good," said Tom Merkel, 12. "He almost won a picture of Ralph. He had to make five foul shots, but he only made four. His last one was a toilet bowl . . . that's when it rolls around the rim."

Sampson's two-day camp appearance -- he will return today -- followed talks by other college and professional basketball players, including Buck Williams, John Lucas and Adrian Dantley.

"I'm not doing much else this summer," said Sampson, who turned 21 last week. "Just lifting weights, doing these camps and hanging around with my girlfriend."

Lisa Payne, 19 a former Wilson High School cheerleader from Washington and a Virginia premed student, accompained Sampson to the gym. While Sampson bantered with youngsters, Payne listened and toyed with her diamond ring, a present from Sampson.

Asked about the ring, she looked to Sampson, who said something to her. "I'd rather not comment about that," Payne then said, smiling.

The camp appearance was a leisurely few hours for Payne and Sampson, who are both glad that the pro basketball draft has come and gone without him.

"It was real tough for a long time, when Ralph was choosing to leave school or stay," Payne said. "It was his decision, though. He didn't talk much about it. He's very quiet about things like that."

Sampson said that this year's decision to turn down Dallas was tougher than turning down Boston a year ago.

"I really went back and forth before I finally decided," he said. "I talked to my old high school coach a lot.

"I'm glad another decision like that won't come around for another year."