Virginia, with a 27-4 surge in the second half, and Brigham Young, on Danny Ainge's dazzling dribbling and layup with two seconds to play, tonight advanced to Saturday's NCAA East regional basketball championship.

Brigham Young, which trailed by 11 points in the second half, beat Notre Dame, 51-50, after Virginia, the Atlantic Coast Conference regular-season champion, defeated Tennessee, 62-48. Cavalier center Ralph Sampson scored just nine points.

Ainge, held in check most of the game by a box-and-one defense, had scored only 10 points until his final heroics, which beat a Notre Dame team that went into a stall midway in the second half.

At the end, after a BYU timeout, Coach Frank Arnold went with three guards. Ainge took the in-bounds pass and dribbled to midcourt where three Irish defenders awaited him. He evaded them with a nifty behind-the-back dribble and continued down the left side of the foul lane. There, Notre Dame defender Tim Andree backed off, avoiding a possible foul, and Ainge went in for a right-handed lay-up, Orlando Woolridge coming over too late to successfully defend. The Irish were out of timeouts and could not stop the clock.

In the opener, Tennessee's game plan was to stop Sampson, which it did, and shoot 60 percent, which it didn't because of Virginia's strong defensive play. Tennessee (21-8) led, 36-31, with 13:15 to play. Then came the Cavalier onslaught -- a combination of man-to-man and zone defenses to make up for Sampson being able to score just one point in the final 30 minutes.

The tactics held the aggressive Vols scoreless for 8:10. Meanwhile, the Cavaliers scored 13 straight points, six of them by Jeff Lamp, the game's high scorer (18 points), to move ahead, 44-36.

"At that point, we hoped Virginia would come out and go man to man," Tennessee Coach Don DeVoe said, referring to when his team led by five. "But a few things went wrong."

The big thing was Tennessee's inability to make shots. Over an eight-minute stretch, the Vols, who had beaten BYU, Arizona State and Kentucky this season, missed all nine shots they took and committed six turnovers.

During Tennessee's slump, Lamp, Jeff Jones and Othell Wilson were running the Southeastern Conference team ragged. And seconds after Virginia took a four-point lead, it dropped back into the tight zone that had been so successful in the first half. It didn't matter. Tennessee was finished.

By the time Vol guard Gary Carter scored from 15 feet out, the Cavaliers (27-3) were flying and on their way to Saturday's 3:30 p.m. game at the Omni. (Lamp scored from the corner; Lee Raker, who again limped in the game with a severely bruised thigh, hit from 25 feet, and Wilson added two free throws to push Virginia to a 50-38 lead with 3:20 to play.

"The key was that stretch when we played our man (-to-man defense) to get ahead," said Virginia Coach Terry Holland. "We struggled a bit near the end of the first half. We were having trouble getting the ball in the basket. . . We got a bit more aggressive in the second half and were able to get ahead."

Once Virginia got in front, Tennessee, which made only 11 of 27 field-goal attempts in the final 20 minutes, had to chase the ball and eventually foul. Virginia closed out Tennessee's season with 10 straight free throws, four of them by Wilson. The Cavaliers led by as many as 18 points before Holland cleared his bench.

"When we didn't hit our shots, the pendulum swung the other way in Virginia's favor," DeVoe said. "Our defense just didn't do the job when we had to. And Virginia made some big plays."

The biggest was probably Sampson's block of a Howard Wood shot while Tennessee was clinging to a 36-33 lead. After the block, Wilson outran everyone downcourt and hit a 10-foot leaning jump shot to pull Virginia within a point. From then on, the game belonged to the Cavaliers.

Virginia had things its way much of the first half, as Sampson, getting the ball where he wanted it, scored his baskets and helped Virginia to a 23-15 lead, which Tennessee closed to 27-26 at halftime behind Wood and Dale Ellis.

"Tennessee began shutting off the passes coming inside and playing pretty good defense," said Sampson, who managed but five rebounds to go with his nine points. "But we hit a few open shots and our changing defenses caught them off guard."

Michael Brooks' two baskets helped the Vols take their temporary five-point advantage before, as Lamp put it, "We decided it was time to play." The senior, hitting eight of 11 field-goal tries, started the 13-0 spurt with a fallaway shot on the baseline and finished a 12-2 run and the final blow with two free throws.

In the second game, Notre Dame had used its final timeout with 24 seconds left to set up its last shot. It obviously wasn't as good a one as Coach Digger Phelps wanted. But Kelly Tripucka made it anyway, a 20-foot, fallaway, high-arching jumper from the corner for a 50-49 lead with nine seconds left.

Then Ainge, who scored 37 points against UCLA Saturday but had only two points in the first half tonight, managed to dribble the length of the court for the game-winner.

A Tracy Jackson jumper had given Notre Dame a 40-29 lead with just over 11 minutes to play. But the Irish elected to sit on the lead and the Cougars began to fight back. Greg Ballif scored six points, including a three-point play to bring the Cougars within a point, 48-47, with 3:34 to play.

After an exchange of missed shots, a missed front end of a bonus free-throw situation by Woolridge and a Ainge walk, Woolridge was tied up at midcourt with 1:17 to play. The Cougars came away with the jump ball and Ballif sank a shot from the top of the key to give BYU its first lead, 49-48, with 54 seconds left. Then Notre Dame decided to run down the clock.