It was 45 minutes after Georgetown had beaten St. John's, 92-80, for the Big East Conference basketball championship tonight, and Chris Mullin, the all-America St. John's guard, was walking out of Madison Square Garden with his little brother, Terrence.

"I need a rest," Mullin said, exhausted from the Redmen's second decisive loss to top-ranked Georgetown in 11 days.

On a night all-America center Patrick Ewing played just 19 minutes for Georgetown and missed most of the key parts of the game because of foul trouble, his teammates flourished, especially on the offensive boards.

The Hoyas outrebounded the Redmen, 36-19, turning 15 offensive rebounds into 24 points, a statistic that St. John's center Bill Wennington and point guard Mike Moses thought even more significant than the Hoyas' 57 percent shooting.

"They went to the boards hard on offense," Wennington said. "We got caught helping out and missing box outs . . . It hurts a little when you think you're doing well, and they don't let down on you. When Patrick got in foul trouble, there wasn't a team letdown. It gets a little frustrating."

Asked if the Georgetown rebounding advantage was a result of the Hoyas' ability or his team's lack of execution, St. John's Coach Lou Carnesecca said, "I don't know. Give them the credit today."

It was partially a result of Georgetown's motion offense playing havoc with St. John's man-to-man defense. When St. John's won the first game in January, the Hoyas' offense was struggling, and they shot just 40 percent. In the last two games against St. John's, Georgetown has shot 58 percent.

"We didn't feel like we were having any trouble getting good shots," Martin said. "When our shots aren't falling you have to play harder defense or hit the defensive boards.

"There has to be some kind of communication, something between the other four guys on the floor, so they know when the ball is going up. That's the thing. We've been more patient the past two weeks."

Of Georgetown's 15 offensive rebounds, Reggie Williams had four; Ewing, Ralph Dalton and Wingate three each and Martin two. Point guard Michael Jackson (19 points, 13 for 15 at the foul line) had none; he was the designated defender to stay back and prevent breakaways.

"We didn't concentrate on boxing them out," Moses said. "They broke our backs with second shots, especially off long jump shots."

The Hoyas also broke the Redmen's backs because Martin far outplayed Walter Berry, his St. John's counterpart, who had 45 points and 23 rebounds in St. John's first two tournament games. Tonight, Berry had 14 points and seven rebounds but wasn't that effective.

Martin (18 points, six rebounds) said he changed his style slightly in defending Berry. As usual, he tried to deny him the ball.

"But when he catches the ball, I wanted to keep him from penetrating in," Martin said. "I didn't want to try to block his shot. I just wanted to get a hand in his face and box him out, because the one thing Berry does very well is follow his own shot.

"I didn't want him to shoot the ball, run in and get the offensive rebound and get a dunk, and they'd get excited, or whatever."

But there were no whatevers for St. John's tonight. "You can't afford to lose next time," said Moses, anticipating a possible fourth meeting in three weeks in the NCAA Final Four. "They're the best team right now. This is over. We're not concerned with Georgetown right now."

Carnesecca wasn't ready to think of another Georgetown game, either. "I think they played almost a perfect game," he said. "Let me think about it (next time) awhile. You get hit in the head, you think about it awhile."