It is a race track maxim that "they all get beat" and today the fastest horse in the United States was beaten for the first time.

Phone Trick, the sprinter who looked almost invincible winning the first nine races of his career, lost to Groovy in the seven-furlong, $111,600 Tom Fool Stakes at Belmont Park this afternoon. It wasn't even close: Groovy took the lead after a few strides and drew away to a decisive 6 1/4-length victory.

Phone Trick had annihilated all of the best sprinters in California as a 3-year-old last season, then came east to extend his winning streak in New York. But today's race figured to be a tough test because of Groovy's presence in the five-horse field. The speedster had been miscast when he ran in the Kentucky Derby and the Preakness, but now he was running at his proper distance and, as a 3-year-old, he had to carry only 112 pounds to Phone Trick's 126.

Phone Trick broke sharply, but after a few strides Groovy rushed up along the rail to take the lead. Jockey Jorge Velasquez was content to sit two lengths behind as Groovy sped the first quarter mile in 22 1/5 seconds and the half in :44 2/5.

But when Velasquez asked for a response, he didn't get one. Groovy was in command of the race when he turned for home and he finished in 1:21 3/5. He paid $7 to win.

Richard Mandella, Phone Trick's trainer, thought his colt had lost because he ceded Groovy the early lead. "The biggest mistake we made today was trying to take him off the pace a little," Mandella said. "We should have let him run his usual style. I told Jorge before the race to let Groovy have the lead if he wanted it and let Phone Trick lay second. We should have let Phone Trick take the lead and run with it and let Groovy catch us. Oh, well, that's life in the big city."

Groovy's trainer Jose Martin and jockey Jose Santos also thought that tactics were the key to the outcome. "I knew Phone Trick wouldn't go out in front with us," Martin said, "so I told Jose to open a big lead. Groovy is learning to relax on the lead now, so that really helped him today."

Still, Phone Trick's running style shouldn't have accounted for his bad performance today. The colt never has given indications before that he is a strictly one-dimensional speedster. If he had given a typical performance on this lightning-fast racing strip, he would have been able to run the seven furlongs in 1:20 or so. The fact that he barely broke 1:23 suggests either that his form is tailing off or that he has a physical problem. In any case, the loss reaffirmed how difficult it is for any horse at any level to keep on winning.