New strains of tuberculosis that defy treatment by the usual drugs have begun to invade urban communities in the United States, according to doctors at the Presbyterian Hospital of New York and Columbia University.

Tuberculosis, an infectious pulmonary disease, has been successfully treated with antibiotics for decades and has been held down to a small number of cases in this country. But while the incidence of tuberculosis nationwide is still declining, said Dr. Harold Neu of Columbia University, it is increasing in immigrant communities around the country.

Though there is little danger to the country at large, patients in immigrant communities are dying of the disease once again for the first time in decades.

In noting the increase in disease around the country, such as in the large immigrant communities in California, Neu reported that among Vitnamese patients in one area, 60 to 70 percent of the tuberculosis cases were resistant to a common antitubercular drug, and 20 percent resistance to three or more drugs were found.

Neu said the situation is a minor threat to those outside the immigrant communities because the tubercle bacillus, the cause of the disease, is very slow growing and is not a hardy bug. It dies quickly in the air. The drug-resistant strains apparently are even less hardy. So tuberculosis is usually passed (through coughing) only in the most crowded, enclosed conditions.

Even when the disease is contracted, it is normally not difficult to treat, though the patient must take antitubercular drugs steadily for a year or two to assure that all the bacilli are killed.

"But recently we have had one woman who died here [in New York]," Neu said, "and another man who had to have part of his lung removed to get rid of the bacteria there -- a procedure we haven't done since the 1950's."

In both cases, the patients apparently had been diagnosed as having tuberculosis some years before but stopped taking their medicine before all the bacilli were killed.

"What happens is that the bacilli left over are the strongest, most resistant ones," Neu said.

Thus the most resistant of the tubercular bacilli grow inside the bodies, and can then be passed to others in a community.

To combat the growing problem, the doctors recommend not only giving the two most powerful (although more expensive) antitubercular drugs immediately in many cases of immigrant tuberculosis, but also conducting tests no longer common to determine if the patient has a resistant tuberculosis.