Freshman Tyren Naulls made four straight free throws in the final 13 seconds today and UCLA upset No. 1 Notre Dame, 56-52, in a game that once again should jumble the national rankings.

The Bruins, ranked third by United Press International and fourth by the Associated Press, served notice they just might have still another national championship-caliber team. And they beat the Irish at their own game: muscle.

UCLA, now 18-3 and playing as well as any team in the country, avenged an earlier 81-78 loss to Notre Dame in Los Angeles. The Irish, 17-3, had prevailed that day by beating up the Bruins inside and wearing them down.

Not today.

UCLA's David Greenwood and Kiki Vandeweghe dominated the boards. And when Notre Dame needed the big baskets down the stretch, it could not get the ball inside for high-percentage shots.

The contest between the two best shooting teams in the country turned out to be a defensive duel.

Notre Dame, shooting 55.5 percent as a team, shot 31 percent in the second half today, missing 20 of 29 shots. The Irish shot 39 percent for the game.

UCLA, shooting 56.3 percent to lead the nation going into the game, hit only 42 percent, but came up with the big baskets when they most were needed.

The biggest points, however, came at the free-throw line and were delivered by Naulls, a 64 percent foul shooter and the nephew of former UCLA and NBA star Willie Naulls.

Roy Hamilton, UCLA's best ball-handler, had fouled out of the game with 2:43 to play and UCLA leading, 48-44, and was replaced by Naulls.

With 21 seconds left, UCLA had the ball and a 52-50 lead.

"We thought we could foul Naulls and get away with it," Notre Dame Coach Digger Phelps said.

Bill Hanzlik fouled Naulls with 13 seconds left and the freshman made both ends of a one-and-one situation, even with most of the 11,345 at the Athletic and Convocation center screaming and those behind the basket waving their hands trying to distract him.

Tracy Jackson scored on an uncontested drive with seven seconds left to get Notre Dame back to 54-52.

The Irish called a timeout and, after UCLA put the ball back in play, Jackson quickly fouled Naulls.

Naulls again made the front end of his one and one. After a UCLA timeout he swished through the second shot to wrap up the game.

"I just tried to concentrate," said Naulls, who stared at the floor until the last possible seconds in apparent attempts to block the crowd from his mind. "You've got a 50-50 chance of making them, so all you can do is shoot them. Luck was on my side this time."

"If he had missed those free throws I think it might have been a different story," said UCLA Coach Gary Cunningham.

UCLA had the jutters early and fell behind, 7-0. They eventually caught up, halfway through the period and trailed, 28-25, at halftime.

Vandeweghe tied the score for the fifth and last time in the second half with a tap-in with 7:49 to play. That made it 40-40.

Then Greenwood, who had been inconspicious except for his rebounding, came up with three straight outstanding plays to stake the Bruins to a 46-41 lead. They never lost that lead again.

Greenwood first drove the baseline around Bill Laimbeer and scored on a difficult, off-balance layup. Then at the other end of the floor, he swatted away Hanzlik's jumper and Hamilton scored on a fast break as a result.

Jackson made one free throw on Notre Dame's next possession, but Greenwood countered that with a drive down the middle and a basket over Bruce Flowers.

That put UCLA ahead, 46-41, with 4:53 to play and Notre Dame never recovered, suffering its first loss at home in 16 games.

Hamilton with 12 points and Greenwood with 11 were the only Bruins to score in double figures while Jackson Kelly and Tripucka led Notre Dame with 11 points each.