For Agassi, the U.S. Open Is Not a Shut Case--Yet : Tennis: Longshot from Las Vegas plays Martin and Stich faces Novacek in today’s semifinals.

The men’s semifinals of the Andre Agassi-U.S. Open tennis tournament will be played today. Actually, Agassi is not a sponsor of the event. He merely owns it this year.

The unseeded Agassi began the tournament as both a Las Vegas longshot and a longshot from Las Vegas.

And in his non-matching blue and black tennis outfit, long straggly hair flowing from under his black cap toward his black socks and black and white shoes, he is a sight to behold.

But he is the apple of tennis fans’ eye in the Big Apple.

“Everybody is talking about Andre, everybody thinking he is going to win, and that’s just the way I like it,” said Michael Stich of Germany, another semifinalist, who will play Karel Novacek of the Czech Republic.

Many believe Stich, seeded fourth, will get through to Sunday’s final and give the tennis world a matchup of former Wimbledon champions, Stich having won in 1991 and Agassi in 1992. It would be strawberries and cream in Flushing Meadow, which, hopefully, would be better than it sounds.

But before either gets to Sunday, when a victory by Agassi would make him only the second man in the history of the tournament--since Vic Seixas in 1954--to take out five seeded players, each must pass a formidable test.

Agassi will play Todd Martin, the other seeded player who got through to the semifinals in a men’s draw as full of casualties as your basic Clipper transaction. Martin, seeded ninth, is the only male to have made it to the semifinals of three Grand Slam events this year. He lost in the final of the Australian to Pete Sampras and in the semifinals at Wimbledon to Sampras.

Martin has played Agassi five times and won three matches, among them a five-setter this year at Wimbledon. At 24, Martin is the same age as Agassi, but he started his climb on the tour much later than Agassi, who, in his early teens, left the bright lights of Las Vegas for the bright lights of the Bollettieri Tennis Academy in Florida. When Agassi was playing Ivan Lendl in the semifinals of this tournament in 1988, at 18, Martin was out on one of the back courts, playing in the junior boys’ event.

Martin, 6-feet-6 and kind of a gentle giant, did the unthinkable and unforgivable for those who are to make it big on the pro tennis tour: He went to college, Northwestern University, and stayed for two years. Nevertheless, it is fair to say that both are educated in the Greek tradition. Martin read Socrates, Agassi read Nick.

On the court, Agassi is an all-court player, capable of rallying with anybody from the backcourt, capable of returning anybody’s serve and capable of serving and volleying, if necessary. He is fast, flamboyant, flashy.

Martin is an all-court player too, capable of playing well from the backcourt and capable of serving and volleying with the best of them. He is not fast, not flamboyant and not flashy. The likely key to this match is that Martin will serve 110-m.p.h. shots at Agassi, who might very well return them at about 115.

The big serve will also be a big issue in the Stich-Novacek semifinal. Stich has a first serve that frequently exceeds 120. Novacek’s is slightly slower but so effective that he hit 28 aces in his five-set semifinal victory over Jaime Yzaga of Peru. The difference will be that Stich follows his big serve to the net, whereas Novacek stands at the baseline and admires his.

They have played six times and Stich has won four matches, on various surfaces. For Stich, who has gone out early in most Grand Slam events since his 1991 victory over Boris Becker in the Wimbledon final, this U.S. Open is nevertheless somewhat familiar territory.

Not so for Novacek, a 29-year-old veteran, who is known for playing lots of tournaments and having lots of single-day successes, but never really breaking through in a big tournament. For him, this is Christmas in September.

“I have been playing masters, I have been playing everything basically that exists in tennis,” he said after beating Yzaga. “But I never went to a semifinal of a Grand Slam, so today I am very happy.”

Novacek, ranked No. 56 in the world, will also be the longest longshot to get through to Sunday. Stich, who has his remarkably fluid game flowing quite nicely now, might be the pick of the savvy tennis insiders. Martin will be the choice and heartthrob of middle America, whose values and style he so clearly represents.

And Agassi? What should he care? He owns this place.