In one of those mismatches that pop up all too frequently in college basketball these days, highly ranked Georgetown routed St. Mary's (Md.), 96-58, last night. But everyone, including the losing Division Iii team, went away happy from McDonough Gymnasium.

The winning Hoyas were pleased because Coach John Thompson finally was able to give his newcomers their first extensive playing time of this 6-0 season, which has seen Georgetown rise to 15th in the UPI and 16th in the qqap rankings.

St. Mary's was happy. As Coach Don Bryan put it, "We don't fool ourselves that we can beat them. We've never held the ball yet . . . We got the socks beat off us, but we enjoyed the game."

The crowd of 2,340 also enjoyed itself, rooting the reserves to the 90-point barrier, which earned the spectators a free soft drink at the Center Cafe on campus. The way they sceamed down the stretch, shouting "Pepper, Pepper," you may have thought the prize was at leasta sixpack of beer.

St. Mary's, now 5-4, stayed with American U. for 20 minutes Wednesday night, before the Eagles pulled away. Last night, asGeorgetown opened in man-to-man defense for the first time this season,the Saints stayed even, mainly on the surerbshooting of guard Mike Ayers and forward Hammond Willis.

Then Georgetown switched defenses, to a 1-3-1 zone, an alignment that has proven especially efective for the Hoyas this season. It was an excellent choice against the Saints, because the small St. Mary's forwards could not see inside and the Hoyas quickly outscored them, 17-2, for 41-26 control.

John Duren made four straight jump shots during the sketch for the Hoyas. During those 12 possessions, St. Mary's, 11-2, at the start of the second half, the Hoyas had a 58:34 lead with 15:48 to play. Shortly thereafter, Thompson started substituting enmasse.

Freshman Eric Floyd led the Hoyas with 16 points, followed by Craig Shelton's 15, Duren's 14 and Steve Martin's 11, the same as reserve Jeff Bullis. No starter played more than 25 minutes tonight. In the first five games, Shelton, Duren and Martin each averaged more than 35 minutes a game.

"The thing that was good tonight," said Thompson, "was that we got an opportunity to use some guys in the ball game that haven't had an opportunity to use some of the bench in the game.

"Because of the tough early schedule, we haven't had the opportunity, like we normally do, to utilize some of the freshmen, to help them blend in. I was particularly pleased with (Mike) Hancock's and Bullis' play, because in order for us to be successful later on in this year, they have to be able to play."

Hancock, 6-foot-7 forward from Roosevelt High, made all four of his field-goal attempts, including the "Dr. Pepper shot" with 1:55 remaining, and collected five rebounds in 14 minutes. He had played only 20 minutes in the first five games.

In addition to his 11 points, Bullis also collected 10 rebounds in 17 minutes. He had played only 20 minutes in the first five games.

In addition to his 11 points, Bullis also collected 10 rebounds in 17 minutes. He had played only 18 minutes in the opening five games, the last three of which were victories over 1978 NCAA tournament participants St. John's.

Bullis and Hancock showed poise and strength on the offensive backboards. Bullis, sick and hurt earlier this season, seemed to tire last night.

But thompson left him in.

"I was pretty much amused by the fact Jeff was tired." Thompson noted. "He's been sick most of the reason for one reason or another. Playing that much time had a tiring effect. He wanted to come out at one point, but I wouldn't let him. I purposely wanted to put pressure (on him) because I want him to get ready to play."

In all, five Hoya newcomers scored career highs as Georgetown won its 18th straight game at home.