St. John's dusted off the strategem that beat Duke in the NCAA tournament last season and, on Reggie Carter's three-point play with five seconds remaining, turned back Georgetown, 71-69, yesterday.

In heavy traffic along the baseline after taking a looping pass from Bernard Rencher, Carter double-pumped, drew a foul from Sleepy Floyd and connected on the 10-foot jumper, silencing a McDonough Gym record crowd of 4,619.

After Carter made the free throw, the Redmen's defense allowed Craig Shelton only a 22-footer at the buzzer in the Big East contest that would have tied the game. The ball counced off the back of the rim.

The play that won the 14-1 Redmen's 12th straight game took them to the NCAA East Regional final a year ago. As St. John's Coach Lou Carnesecca put it, "It's so nice to be able to go to him on plays like that." c

Carter's foul shot gave the 6-foot-3 guard 21 points.

"We went to him," Rencher said, "because he's our money man."

"I've been there enough," said Carter, a fifth-year senior who was drafted by the New York Knicks in the second round of last year's NBA draft. "I've got the experience, I Know what to do with it. I can get something out of it."

He did, giving St. John's a 4-0 Big East record and a strong shot at the first-round bye in the league tournament, since the Redmen play Syracuse at home. Georgetown is 10-5 overall, 1-1 in the Big East.

It was only the seventh McDonough Gym defeat for the Hoyas in five years, while they have won 61.

As in a one-point loss to Boston College in the Holiday Festival, the Hoyas were caught between defenses at the end. Coach John Thompson, generally pleased with his team's performance yesterday against a top-10-ranked opponent, called a full-court zone press, dropping back to a 2-3 zone.

A Shelton-al Dutch trap in the press almost resulted in a steal from Rencher. But he escaped and the Hoyas were partly zone and partly man to man on the play that resulted in Carter's winning shot.

"I was on him one on one," Floyd said. "I turned my back on him. I guess I bumped him."

In the air, after his second pump, Carter said, he heard umpire Art Mellace's whistle. "I knew I'd drawn the foul," Carter said. Then he changes his shot it dropped.

"He threw one up," said a disappointed Floyd. "Sometimes they go in, sometimes they don't."

Georgetown had streaked to an 11-0 lead and received a career-best performance from 7-foot center Mike Frazier, who had replaced injured Ed Springgs, but now had to call a timeout at midcourt with three seconds to play to set up its final shot.

"I definitely thought they were going to Floyd," said Carter, who guarded the Hoya sophohmore on the inbounds pass. "Everybody thought they were going to Floyd."

Thompson said later that Floyd was Georgetown's first choice to get the ball. He was supposed to come around a double-pick on the left side and take a baseline route to the right corner, but Carter shadowed him so closely that trigger-man Dutch had to go to his second option.

That called for John Duren to set a screen for Shelton, who was going across the lane. Shelton was over-played so well by Frank Gilroy that he had to take the ball on the right side of the key, about 22 feet from the basket.

"It was a good pick by Duren and I was open," Shelton said. "I didn't have time to do anything else but shoot it . . . I went too far out from the basket."

Said Thompson: "With three seconds on the clock, you can't take a vote."

Georgetown, now has collected as many losses as it did in its best-ever campaign in 1978-79. Although the Hoyas lost in the second round of the NCAA tournment to Rutgers that year, they were acknowledged as the best team in the East.

That team had exceptional poise and a knack for winning the close games.This team is 0-3 in games decided by two points or fewer. What hurt the Hoyas yesterday more than anything (other than Carter's winning play) was too little offensive patience late in the game. Poor shot selection resulted in 32 percent accuracy in the final 20 minutes when the Hoyas got 10 more shots than St. John's.

Thompson has substituted freely in the first halves of games this season. Against the Redmen, he did it again, and seemed to break his team's momentum when it had gone ahead 13-2.

"When you play a good team," Thompson said, "the first five to 10 minutes does not establish momentum. What better time is there to rest your guys when you're running and pressing? I wanted to use a lot of players so we wouldn't be worn out at the end.

"It's a disappoint loss, but I'm not disappointed in the way the kids played."