Know how you're driving down the road and suddenly, out of nowhere, some turnip pulls his junker crossways right in front of you? Your heart stops, you forget to breathe and goose bumps jump out on your arms. Physiologists call that the "startle reflex." In college basketball, it ought to be the Sampson Effect.

Al Campanis, the talent guru of the Los Angeles Dodgers, stood at the plate 20 years ago to look at fast balls thrown by a kid left-hander. He never forgot what happened. As the baseballs came by, laser beam-quick, the hair on Campanis' arm rose. "That's happened to me twice," Campanis said. "Once in the Sistine Chapel, when I saw Michelangelo's ceiling, and the first time I ever saw Sandy Koufax throw."

Ralph Sampson can do that to a guy. Time after time today, Sampson did some startling, majestic thing. The numbers say he had 30 points and 19 rebounds against the No. 1-ranked team in the country. The numbers only suggest the wonder.

Sampson's team, Virginia, rated No. 2, lost as gorgeous a game as you'd want to see, with Carolina rallying late to win, 65-60. This is January, ages away from March when it all really matters in the NCAA tournament. So the game, to one bedazzled witness at least, became secondary to the basketball miracles worked by Sampson.

He is 7 feet 4. Remember that. It is remarkably easy to forget as you see Sampson. His movements are so graceful, so economical that when he takes his first shot of the game from 20 feet, it doesn't seem remarkable that the shot goes in. Then you remember, my word, Sampson is 7-4 and throwing them in from downtown.

Without Sampson today, Virginia loses by 20. Without Sampson, Virginia is an ordinary Atlantic Coast Conference team. But with him, Virginia showed it is good enough to give credence to Sampson's postgame insistence that his Cavaliers didn't lose anything today.

"I think we may be the best team in the country," he said. "I'm not going to put us down just because we lost today . . . They didn't take anything away from us."

If Dean Smith can find another scorer, this is the year the coach wins the national championship he deserves. The North Carolina program he has created is as classy as you're going to get. When the customers in Carmichael Auditorium chanted a barnyard obscenity, Smith hurried to the public address microphone and said, "No profanity. Let's do it the right way."

Carolina was behind by eight points then, with 13 1/2 minutes to play.

"It's his gym," Sampson said with a smile. "He can do what he wants to."

Well, not quite. As good as Carolina is, as mighty as its big men, James Worthy and Sam Perkins, are, Smith's team couldn't do anything about Ralph Sampson. Only Virginia's mediocre outside shooting allowed North Carolina to win. The Cavaliers' three primary guards made six of 17 shots and didn't score from outside until the final, hopeless seconds.

The obvious strategy against Virginia is to surround Sampson and dare the other guys to beat you. Smith, a master tactician, sent Perkins man to man against Sampson; he used a box-and-one zone, ensuring the presence of three defenders within an arm's reach of Sampson, and he ordered Perkins and Worthy to deny the entry pass to Sampson.

Against these specialized defenses, Sampson scored 30 points in a 60-point game. When the NBA fined the San Diego Clippers' owner $10,000 this week for saying he might like to finish last and thereby get draft rights to Sampson, the fine was punishment for having damaged the league's integrity. It was not for being stupid. Sampson will make an NBA team great.

You could write a poem about each of 20 plays Sampson made today. He scored from 20 feet; he dunked left-handed; he slithered along the base line and made a falling-out-of-bounds 15-footer; he dunked with both hands on a 30-foot alley-oop pass; he made two beautiful passes to set up layups. That was on offense. On defense, he rendered Perkins ineffective and even made life miserable for Worthy.

So someone went up to Virginia Coach Terry Holland and asked the real bright question: "How'd you think Ralph played?"

Which is like asking if Ann-Margret is a woman. Some things are obvious. "I thought he was effective," Holland said wryly.

Sampson was too modest about his day's work. He said it's a team game and if he scored 100 points in a loss, it wouldn't be a good day. "I was just trying to play my role and do what I have to do."

Holland said Sampson was subjected "again to a helluva physical beating," but Sampson shrugged it off. "I'm not taking any more than I'm giving out," he said.

Was this the best game of his career? Or is that his 40-point performance against Ohio State last year? "Everybody says Worthy and Perkins are so great," Sampson said. "They're two good players, but they're not all-world. I'm not all-world, nobody is all-world. I just happened to get the points I got because I took it to them."

But wasn't it fun? Every play more startling than the last: doesn't that get to be a kick? "You play because it's fun," Sampson said. "That's in the back of your mind, but during the game you're thinking of what you have to do next. You don't enjoy it until you win."

Oh, one thing more. Sampson played with a broken finger on his shooting hand.