Federal tuberculosis officials say 1990 was a bad year, with possibly the worst TB increase on record. Even more distressing, they say, is the appearance of a strain of the disease that is resistant to anti-TB drugs.

The 1990 U.S. tuberculosis count stands at 23,720, with a thousand or more case reports still likely to come in, according to Dr. Dixie Snider, chief of the TB division at the Centers for Disease Control.That leaves the preliminary 1990 count already higher than the final count of 23,495 cases in 1989. And 1989 was bad enough with a 5 percent increase in the chronic lung disease, the biggest jump in TB since the CDC began counting in 1953.

"It's obviously disturbing," Snider said in a recent interview. "It's completely unprecedented in what tuberculosis has actually been doing since the last century."

What TB had been doing, for the most part, was going down. The disease affected millions before drugs to combat it were developed about 30 years ago.

Effective drug treatment sent TB rates declining sharply. But HIV - the virus that cripples the immune system and causes AIDS - has triggered a turnaround that health officials are trying to stop.

While most people who become infected with the TB germ will never become ill with the disease - and millions in America are in that category - people whose immune systems are weakened by HIV are more susceptible to getting tuberculosis.

Health officials estimate that 1 million or more Americans are infected with HIV.

Adding to the problem, Snider said, is the apparent increase in drug-resistant TB - cases of TB which have developed resistance to the most common anti-TB drugs. A Miami hospital, Jackson Memorial, reported 29 drug-resistant TB cases last year, and the total could grow to 70 or 80 by the time reporting is complete, Snider said.

"That's the most disturbing thing that's happened this year," Snider said. "If they (drug-resistant TB germs) take over and become a significant part of the pool of tuberculosis organisms that are out there, our whole strategy for TB treatment and prevention has got to be completely revised."

She said the worst-case scenario would be for a drug-resistant strain to become dominant.

"It would be a disaster," Snider said. "We wouldn't be able to cure the patients; we wouldn't be able to render-them non-infectious."

To combat the TB boom, Snider said, health officials are attacking on two fronts: drug treatment centers and prisons.

"Those are the places we can identify people with TB and HIV infection," Snider said.