Wyoming was not impressive in its first-round NCAA game Thursday night. Its 61-58 victory over Southern Cal was a gift, with USC losing a late lead while a Wyoming reserve turned into a 17-point hero. Wyoming's all-America forward, the 61 percent shooter Bill Garnett, was 3-for-12 nervous. His coach, Jim Brandenburg, said, "We have to play better against Georgetown."

"They did not play as well as they are capable of," said John Thompson, the Georgetown coach. "Garnett was tight and his shots weren't dropping, so he got tighter."

In the perverse way of basketball brains, Thompson sees danger in Wyoming's off night.

"That's the advantage of playing a first-round game," said the coach whose team is top-seeded in this West Regional and so earned a bye into Saturday afternoon's second round. "They'll be getting loose now."

Georgetown worked out an hour in the Utah State Spectrum today, after which Thompson said guard Freddie Brown took part in his first full-speed scrimmage since his left hamstring tightened in the Big East tournament. Brown left today with two ice packs for the 70-mile ride to the Hoyas' hotel in Salt Lake City.

The last time Wyoming and Georgetown met, the 1943 NCAA championship was Wyoming's reward for a 20-3 game's-end rally that produced a 46-34 victory at Madison Square Garden. The NCAA was only 6 years old then, and weak competition for the more prestigious National Invitation Tournament. As the NCAA grew in stature, Wyoming and Georgetown shrank.

After 1943, the teams won only a single NCAA game in 36 seasons. Wyoming went 1 and 12, Georgetown 0-3 until it won twice in '80. When they meet in this dazzling mountaintop town, they will have come full circle. Georgetown (26-6) is a top championship contender, and Wyoming (23-6) has a second straight title in the demanding Western Athletic Conference.

To picture Wyoming, Georgetown fans must conjure up a familiar Big East enemy that beat the Hoyas once this season: Connecticut. Wyoming is the Connecticut of the West, only more so.

As Connecticut fills the court with behemoths, so does Wyoming. The Cowboys' inside men are 7-feet, 6-10 and 6-9, averaging 232 pounds. Garnett is the little guy there, but he's big everywhere else, scoring 18.6 and leading in rebounds with 8.3.

The team's second-best weapon is guard Mike Jackson. He's scoring 12.9 on 56 percent shooting, mostly from outside.

The offense is all right. Four starters shoot better than 50 percent in a deliberate game that produced scores such as 27-25, 39-37 and 43-37.

But Wyoming's defense wins.

A 2-3 zone is the foundation of a unit that led the nation in defense against shooting. Wyoming's opponents shot 39.4 percent. They averaged 51 points a game, only twice scoring 70.

Wyoming's hustling big guys take up spots under the hoop while the guards harass anyone who moves.

The Cowboys also led the nation in rebounding margin, taking 10 more rebounds a night than the enemy.

All this worries Thompson.

"They pack that zone in the lane with those large, very physical players, and they give you the outside shot," he said.

And Thompson's gang can't shoot straight. It has one guy over 50 percent, Patrick Ewing, who stuffs his baskets. Forced to play a set offense against a big-men zone, Georgetown could be in trouble.

"We have to apply pressure with our press," Thompson said, "and make it a full-court game. If we let them pack that zone into the lane, we're not going to get many second shots."

If Georgetown's press is effective, and it should bother the slower Cowboys as it befuddled speedy Villanova in the Big East championship, the Hoyas can make this the game they love: transition.

The Wyoming coach, Brandenburg, knows that. "We have to make them play our style. We certainly can't run with them."

The unexpected hero of Wyoming's first-round rally was forward Mark Wrapp. The 6-8 junior, averaging only five points with a season high of 12, scored the Cowboys' last nine points.

Wyoming isn't counting on an encore, but the 4,500 Wyoming fans who will make the 500-mile trip here are aware of what happened the last time Bill Garnett had a bad day.

Garnett scored four points in a 39-37 victory over Hawaii the last week of the regular season.

Two nights later, he had 30 points and 16 rebounds in a 66-64 overtime victory over 20-game winner San Diego State.

One thing more. These teams have played four common opponents: Wyoming lost to Missouri, 64-54, and Nevada-Las Vegas, 69-58, but beat San Diego State twice and also American, 71-63. Georgetown beat them all: Missouri, 63-51; UNLV, 76-52; American, 75-63, and San Diego State, 71-53.