By this time most years, the stallions here are working overtime. Not now. A veneral disease has been discovered in perhaps as many as 72 thoroughbreds. Nearly all breeding has been stopped for at least another week. If breeding is prohibited all year, a possibility, the economic loss could run into hundreds of millions of dollars. Panic fills the boudior of the Bluegrass.

"Our loss could be in the millions," said Brownell Combs, master of Spendthrift Farm, a 4,000-acre piece of heaven that is home to 33 of the world's great studs and 120 mares.

"Take Wajima" he said, naming a stallion recently syndicated for $7.2 million. "He'll service 50 mares a season at $50,000 each. Trat's $2.5 million. And Caro. He goes for $30,000. That's $1.5 million. We lose all that. And we'd lose sales on yearlings next spring because we'd have no crop to sell. That's about $2 or $3 million. In other words, it could be a disaster."

That's putting the worst face on it. In a week, all breeding may resume here if tests show the disease has been isolated in those 72 lovers. The two-week delay, then, will have ruined the precise schedules for breeding, but that is a small price to pay when the alternative is, in combs' grim words, "out of business."

Combs is a central figure in this drama. Many people believe he started the whole thing by importing the stallion Caro from France last fall. The veneral disease - contagious equine metritis, CEM for short - struck in Ireland, England and France the last two years. All imports of horses from France were to end the very day, the very hour, that Combs chartered a cargo plane and whisked Caro across the Atlantic. Combs was delighted then with his coup, for Caro was proven one of the world's leading sires, daddy of horses that won $1.5 million last year.

Well, Caro has it.

Combs insisted he's getting a bad rap. He said he did everything possible to make sure Caro was free of CEM. He said the stallion underwent extensive testing upon arrival in the United States. All tests were negative, Combs said, and the U.S. Department of Agriculture approved Caro's entry. Now Combs finds himself under attack by other breeders. "A large portion of them are acting like snakes," he said bitterly, and he said it's all he USDA's fault.

"The USDA now admits its tests for CEM were invalid," Combs said. "Everybody is wanting to hang Gainesway (another farm that also imported a stud from France) and Spendthrift. But if I had it to do all over again, I wouldn't change a thing. I'm proud to be standing Caro here at Spendthrift. I'm sorry that he brought the disease, but I'm sorrier the USDA doesn't know what the hell it's doing."

And because Caro has GEM, two mares here became infected. The disease is highly contagious, being transmitted by anyone in contact with the horse. In Europe's it's called "vet's disease" because veterinarians often become carriers of the bacteria that produce intense inflammation of the female's reproductive system. The stallion shows no symptoms. He simply delivers the disease.

With treatment, CEM is cleared up, quickly but its danger is that it can prevent impregnation or cause aborted pregnancies. Soon enough, CEM showed up at several farms in the Bluegrass and all movement of horses for breeding was prohibited. Caro and five other stallions are not allowed out of their stalls.

The problem is, CEM is a new disease and nobody really knows what they're doing, said a USDA veteriarian who has worked on the Kentucky cases. The tests on Caro were not correct, said Dr. Presley Winner of Frankfurt, Ky., and the suspicion is that the CEM bacteria vanished from the test specimen because it took too long - perhaps three days - to transport the specimen from Kentucky to a laboratory in New York. Now the CEM tests are being done here at the University of Kentucky.

What worries Combs now, he said, is the possibility CEM has spread beyond the known cases. With Caro, 469 other stallions and broodmares were imported from Europe in the last 18 months. If the test of Caro were reported negative and he yet had CEM, what about the other 469? Combs paints a picture of a national epidemic, with CEM everywhere from Florida to Virginia to California. The USDA man, Winner, said "We haven't heard of anything anywhere else - so far."

Thoroughbred breeding is a billion-dollar industry in Kentucky, according to Bill Coman, executive director of the Thoroughbreed Breeders of Kentucky. The state has about 425 stallions and 7,500 broodmares. Small wonder, then, that Brownell Combs is seen as the villain who endangered everyone's will-being by flying Caro out of a CEM nest at the last minute. He understands that, but he thinks it's irresponsible and, worse, ungentlemantly to point fingers of blame at Spendthrift.

"Other than not bringing Caro here, there's nothing else I could have done to prevent this," Combs said The USDA's Winner said nothing suggests that Combs tried to sneak Caro in without the proper testing. Combs showed a detalied, printed record of Caro's testing. "All negative tests," Combs said.

But other horsemen were angry, anyway. "All of our competitors are happy to see us like this," said Combs, 44, who three years ago took over direction of Spendthrift from his father, Leslie Combs.

"This game isn't played in short pants. But Spendthrift does everything in its power to help the breeding industry. In no way would we do anything knowingly harmful or detrimental to the industry, because if you're a leader, you don't do that. Now, instead of wasting time and pointing fingers, we should all pull together. There's been enough screaming and shouting."

Kentucky's immediate answer to the CEM epidemic is another quarantine of the 72 horses suspected to carry the disease. The ban on movement of horses between farms will end next week - provided no new cases of CEM appear. The 66 mares now quarantined will not be bred at all this season. The stallions will go back to work when certified healthy by tests done this time at the local university lab. Combs said Spendthrift set up its own lab with its own technicians to expedite testing.