Marfa had just worked a swift half-mile to complete his serious preparations for the Preakness when Wayne Lukas saw the signs that make every trainer shudder.

"Oooh, I don't like that," he said as Marfa took the first telltale bad steps as he walked back to his barn. Lukas was about to discover that the colt had suffered a quarter crack, a half-inch crack in the wall of his left front hoof and, although it will not keep him out of Saturday's race, it could certainly hurt his chances of winning.

At first, Lukas feared the worst. "Your major concern is that it's an ankle, a knee or a tendon," he said. "But when he came back to the barn, I saw the little ooze of blood in the crack." When he did, his distress was mingled with relief, because the crack had occurred in a part of the hoof where it could easily be patched. Lukas summoned his blacksmith, Steve Priborsky, who had just flown back to California after putting new shoes on the colt Tuesday.

"What he'll do," Lukas said, "is to lace the crack back and forth, like a shoe, with piano wire, and anchor it with pins on both sides. Then he'll put a piece of acrylic on it. It goes on like putty, but it hardens in a minute, like the stuff dentists use. And it's like a tooth: it hurts like hell if you expose it, but once you fill it, you can bite down 15 minutes later. The beautiful thing is that if you patch it, the horse can go to the track an hour later."

But how will it affect his performance? "It's no detriment," Lukas said.

Seven of Lukas' horses suffered quarter cracks in California this winter, and are running with patches like the one Marfa will get. But the trainer also conceded that if this had happened to a colt who was getting ready for a routine allowance race, instead of a once-in-a-lifetime chance to win the Preakness, he probably wouldn't even consider running him.

In fact, no one can really assess whether the quarter crack will hurt Marfa Saturday and, if so, how much. This is a crucial question, because in every other respect the colt seemed to be getting ready for a top performance.

In the Derby, he seemed to have overcome the tendency to lug in during the stretch run that had gotten him disqualified once and earned him the sobriquet Marfa the Mugger. "It was just a matter of seasoning," Lukas said.

While the colt was learning his lessons at Churchill Downs, the trainer was learning something, too. "We got a line on all the horses' ability," he said, "and we realized that we can't lay 14th on the backstretch and spot Sunny's Halo and Desert Wine 15 lengths and run them down. We've got to change our strategy and, fortunately, Marfa has the ability to lay closer."

That was the goal of today's workout. It was intended to sharpen Marfa's speed--"put him a bit more on the muscle"--and the colt did what he was supposed to, working a half-mile in a sharp 46 2/5.