It should be a great sports story when Georgetown goes up against St. John's in the NCAA basketball semifinals today, and it might be a great fashion story, too. Just look for the T-shirts.

When Georgetown center Patrick Ewing played a game with a cold 3 1/2 years ago, he wore a T-shirt under his uniform jersey. The 7-foot senior has worn one ever since, and this season the look has even spread to high school teams.

Did Ewing start a trend? Has there been a rash of colds?

Jim Marchiony, director of media services for the NCAA and former sports information director of Georgetown University, advocates the trend theory. "Other players are wearing T-shirts because Pat made it fashionable," he says. "They wanted to emulate him. Now you see high school kids wearing the T-shirts. Pat has a huge influence on young players."

Others aren't so sure. Katha Quinn, in the sports information office of St. John's University in New York, says senior guard Chris Mullin wears a T-shirt because he likes it. "I also think he looks better with it on," she adds. "He wore it last year and then stopped at the beginning of this year. But he wore it for the Pitt game because it got cold in the field house."

St. John's coach Lou Carnesecca first wore his famous lucky sweater at that January game, for the same reason -- a chilly basketball court. When the victory over Pittsburgh started a streak of 13 wins, Carnesecca continued to wear the sweater and Mullin his T-shirt.

Earl (The Pearl) Kelley, a junior guard at University of Connecticut, says he probably donned a T-shirt for the first time in his freshman year. "I tend to get sick easily, and some of the field houses where we play are really cold," he says. "The T-shirt takes off some of the sweat, and you have less chance of catching a cold.

"I probably wore a T-shirt for all except the first couple of games this season. Those were played at home, and our floor tends to get hot. But after I wore it once, even if the temperature is perfect, there's something psychological about taking it off. If you've been winning, why take it off?

"Also," Kelley says, "after a while it's an attention getter. You notice the guy in the T-shirt. I don't want to speak for anyone, but I'm sure that's why Pat wears one, too -- he must be over that freshman-year cold by now. He started wearing a T-shirt at the same time he began to really blossom as a player. So why ruin a good thing?"

Assistant coach Dan Hewins of DeMatha High School in Hyattsville describes the trend among high school players as a "double-edged sword. Students identify with the college players who wear the T-shirts. But we also play in some very drafty gyms, where it is easy to catch a cold."

"I don't care for it," says coach John Wood of Spingarn Senior High School, "unless the player is getting over being sick." He also believes the high school players took to T-shirts to "emulate others."

Attention-getter or preventive medicine, this is one trend that has regulations. "The T-shirt must be the same color as the uniform," says Kathleen Hatke, an assistant in the legislative services department of the NCAA. An athlete is also forbidden to wear any commercial trademark or logo on a T-shirt. "The membership of the NCAA does not want to be in the position of an advertiser," Hatke explains. That rule was enforced in 1983, when Ewing was told he could not wear a Nike T-shirt on the court.

When he's drafted by the NBA, he'll have another rule to reckon with -- the regulation requiring that everyone on a team wear the same uniform. Or maybe Ewing will persuade his teammates to adopt his trademark.