With 100-degree heat and high humidity choking the Washington area yesterday afternoon, conditions seemed fit for neither man nor beast. But for jockeys and horses at Laurel Race Course, they had to be accepted.

Laurel completed a 10-race program with no on-track hardships. (Wednesday, Memorable Sal collapsed from heat exhaustion after winning the second race but later walked away.) Throughout the day, however, precautions were taken. Grooms carried buckets of water as they led horses to the paddock; hoses were made accessible near the track, and even weight-conscious jockeys took liquids to prevent dehydration.

"It's absolutely terrible," jockey Alberto Delgado said after his second victory of the day. "During the race, it's okay, but afterward you feel like you're going to get sick."

According to state veterinarian Pat Brackett, fitness, fluid intake and electrolyte balance are integral in helping horses withstand the heat. She said those who receive Lasix, a diuretic that helps control respiratory bleeding, face greater risks because they're more prone to dehydrate.

As trainer Scott Regan watched one horse parade through the paddock, he said: "This horse has probably been sweating all morning, he's sweating now, and he going to go out there and run. A horse might lose 20 or 30 pounds on a day like today. You simply can't run a horse as often under these kinds of conditions. You train them light, and you hope."

"If a horse normally gallops two miles in the morning, you'll probably cut back to one mile," said trainer Jerry Robb. "You try to get them out early, before it gets too hot."

Gregg McCarron said he expected to lose 2 1/2 to three pounds simply from riding in three races. "It's miserable out here, but it's a little easier on us," he said. "We can get out of the heat. These poor {horses}, when they're done running, they've got to go back to the barn" where it's not always cooler.

On days like this, said trainer Jo Owens, "You just try to keep as much water on them as you can." Fat And Foxy Retired

Fat And Foxy, an $18,500 claim who became one of the best Maryland-bred 3-year-old fillies in 1988, has been retired. Owner Arthur Benjamin said his stakes-winning mare, who earned almost $250,000, will be bred to Bet Twice. Rosecroft Cancels

Rosecroft Raceway canceled its 11-race card last night after a thunderstorm caused severe flooding in the track's clubhouse. All races on the card were scrapped except for a leg of the Baltimorean series for 2-year-old colts, which will be run as the 13th race tonight.