Although Broad Brush had not looked overpowering against lesser opposition in Maryland, trainer Dick Small thought he deserved a shot in the Wood Memorial Stakes today. He said his colt "goofed off" whenever he got to the lead, and thought he would show the true extent of his ability when he had to meet some of the country's best 3-year-olds.

This sounded like wishful thinking, but Broad Brush made his trainer look like a prophet. He won the $297,500 Wood Memorial by a half-length over Mogambo and established himself as a legitimate contender for the Kentucky Derby two weeks from now. In the process, he tarnished the Derby credentials of both second-place Mogambo and Tasso, the 4-to-5 favorite who finished fourth.

Broad Brush today displayed the same combination of speed and tractability that had carried him to six victories in eight previous starts. When Groovy went to the lead, as expected, Vincent Bracciale Jr. put Broad Brush into a perfect spot, sitting second behind the faint-hearted speedster. Mogambo and Tasso raced on the outside, within reasonable striking position.

Groovy, ridden by Craig Perret, set a moderate pace, covering the first half-mile in 47 2/5 seconds and the three-quarters in 1:11 1/5, then started to weaken on the turn. As he did, Broad Brush drew abreast of him, but neither of the favorites was accelerating.

In midstretch, Broad Brush had taken command of the race, and looked as if he were not going to be threatened. And then, suddenly, all his pursuers started to gain ground on him. Apparently he was goofing off again, ceasing to extend himself once he had the lead. Even Groovy, who had been left for dead, was closing in. "This colt does the same thing in all his races," Bracciale said. "He scared me in the last part, but I have a lot of confidence in him."

Broad Brush needed a ridiculous :14 2/5 to cover the last eighth of a mile, but he managed to hold on and win at odds of 7 to 1. His final time for the 1 1/8 miles was an unimpressive 1:50 3/5.

As he decelerated, jockey Jacinto Vasquez was able to rally Mogambo to finish a respectably close second, Groovy was another neck behind in third and Tasso 1 1/4 lengths farther behind in fourth. Mr. Classic, an 80-to-1 shot, was fifth, followed by Tinchen's Prince and Glider Pilot. All carried 126 pounds.

The relatively close finish may embolden the trainers of Mogambo and Groovy to think they have legitimate Derby contenders, but their horses' failure to make up more ground during the slow stretch run discredits them.

Tasso, wearing blinkers for the first time in three starts this year, ran so poorly that it was hard to find any rationalization for his performance.

"He just didn't run his race today," jockey Laffit Pincay Jr. said. "I don't know why." Trainer Neil Drysdale said: "What is uppermost on my mind right now is making sure that my horse didn't hurt himself. I am not sure why he dropped back when he was in such good position halfway through the race. The Kentucky Derby is always in our minds, but I want to make sure he is okay."

LeRoy Jolley, Mogambo's trainer, said he plans to ship the colt to Kentucky Monday morning.

"Mogambo ran a good race and just couldn't get there," Jolley said.

If the losers were trying to look on the bright said, Small was trying to contain his enthusiasm for the colt who now has boosted his earnings to $565,443. Until today, the biggest win for Broad Brush, a Maryland-bred son of Ack Ack owned by Robert E. Meyerhoff, had come in his previous start, the Jim Beam Stakes at Latonia March 22. Meyerhoff is the brother of Harry Meyerhoff, whose Spectacular Bid won the Kentucky Derby and Preakness in 1979.

"We came here to see what kind of horse we have," Small said, "but it certainly was a pretty slow race, so I'm still kind of wondering just what I've got. I can't say right now for sure whether we're going to the Derby or not, but we'll be thinking more seriously about it."