Later this fall, when Troy Dalbey finally shows up for class at Brigham Young University and the professor asks, "OK, Mr. Dalbey, why couldn't you be on time like everybody else?" Mr. Dalbey will have the perfect alibi; the excuse every kid dreams about.

"Sorry," he'll be able to say, "I was at the Olympics winning a gold medal."It wasn't his fault they scheduled the Games of the 24th Olympiad during the middle of fall semester, was it? He had no choice but to put his schooling on temporary hold and travel with the U.S. swimming team to Seoul - in the hopes of favoring the natives there with repeated playings of the American national anthem.

That anthem played loud, long and clear Wednesday afternoon (Tuesday evening in the United States) at the Olympic Swimming Pool as Dalbey and his 4x200 meter relay teammates mounted the parastyle and received their gold medals for beating the world and the world record. The Americans' combined time of 7:12.51 shaved more than half a second off the world mark of 7:13.10 set by West Germany in 1987 - and was more than enough to relegate the East German team to the silver medal (at 7:13.68) and the West Germans to the bronze (at 7:14.35).

Dalbey and teammates Matt Cetlinski, Doug Gjertsen and Matt Biondi sang the words as the anthem was played, and it was up to Dalbey - at 20, the youngest of the four U.S. swimmers - to get all choked up and have a hard time finishing the song.

"I get a lump in my throat when I see others up there," he said. "I guess I should get one when I'm up there. `The Star Spangled Banner' has never sounded better than that to me. I mean, how blessed can you get? How many people get one of these?"

He was feeling no pain now, which was more than he could say during the last 25 meters of his opening leg. He had gone out extremely fast, leading the eight-man field at the 100-meter turn in 52.50. And he had paid for it at the end, fighting oxygen debt before touching the wall at 1:49.37 and sending Cetlinski onto the second leg.

It turned out to be more than an adequate start for the U.S. team, as Cetlinksi, Gjertsen and Biondi all proceeded to record lifetime bests at 200 meters. Biondi, who missed winning a gold medal in the 100-meter butterfly earlier in the day by .01, raced in redemptive fashion, clocking 1:46.44 on the anchor leg. By comparison, in the 200-meter freestyle individual race two days pervious, when he won the bronze medal, his time had been 1:47.99

Dalbey had been seventh in that final, in 1:48.86, and was not happy about what he called "a timid start."

"So this time I guess I started out a little too excited," he said, smiling anyway. All's well that ends in a world record at the Olympic Games.

All the hours and days and months and years of waging a continual battle with chlorine had been worth it.

"The Olympics kept me in my sport," said Dalbey.

He had gone on record 11 years ago, when he was 9, that the world should watch out in 1988. He had taken second in a 50-meter freestyle event at a regional all-star meet in Casa Grande, Ariz. When the local paper interviewed him about his goals, he came out with, "I'm going to swim in the Olympics in 1988."

Now _ after one more try at a medal in these Games (the 4x100 relay on Friday) _ he's putting the world on notice again. At the Barcelona Games in 1992 he will be 24 and in his prime.

"I'm just a young guy here," he said. And I've always been a late bloomer. If all goes well, I should get stronger and better."

Dalbey transferred to BYU this year from the University of Florida, where he spent his freshman season. Actually, to say he's transferred to BYU is getting ahead of the story, since he hasn't officially enrolled yet.

He plans to start classwork for the winter semester and, hopefully, compete with the Cougar swim team through the WAC season and into the NCAA championships next spring.

"I've applied for a full release from Florida, and from what my coach there (Randy Reese) says, it looks good, that I'll be able to get an appeal from the NCAA and swim this year," said Dalbey. "I want to swim with BYU as fast as I can."

But certainly no faster than BYU _ hardly a household name in collegiate swimming _ wants Dalbey.

He is not enrolling at BYU because of the swimming program. He joined the LDS Church a year ago _ in his hometown of San Jose _ and wants to attend the church university. Also, he has a girlfriend at BYU.

"I already have an apartment in Provo. I should be there in early October," he said.

That will give him better than a month to get moved in and to introduce himself to the swimming coach and the guys on the team. And if any of them wonders who the new guy is and why he got to miss practice, he can start by saying, "Well, they were having this meet in Seoul, and . . ."