Fairfax and Prince George's counties have adopted new procedures for screening foreign-born public school students for tuberculosis, area health officials say.

In Fairfax, foreign-born students entering public schools for the first time will be required to undergo a skin test to determine whether they have been exposed to the disease.

In Prince George's, school authorities this year will begin to urge new foreign-born students to take the skin test.

Officials in both jurisdictions say the new policies spring from figures showing the incidence of exposure to TB is much higher among foreign-born students than among students born in this country.

"It made us uncomfortable," said Dr. Fred J. Payne, assistant director of the Fairfax County Health Department.

"It indicated there was a large body in our school population that we weren't aware of."

In May, a 17-year-old Korean girl who had attended both Fairfax High School and McLean High School died of a heart attack, and tests showed that she also had TB.

Skin tests on students at the two schools after the girl's death showed that about 15 percent of foreign-born students had been exposed to TB.

About 1 percent of the American-born students had been exposed, according to Payne.

None of the 80 students who were exposed to the disease have contracted tuberculosis, a contagious disease that can devastate the respiratory system. Doctors say that is common; those exposed to TB can carry the dormant organism for years without contracting the disease.

Tuberculosis was once a widely feared and often fatal disease, but is now controlled through antibiotics.

"There's no real threat," said Payne. "We just don't want to let it get out of hand."

Policies for screening students for TB vary in the Washington metropolitan area. The District and Alexandria both require all entering students to be tested for exposure to the disease.

Montgomery County implemented a policy three years ago requiring tests for all foreign students coming from a country whose rate of TB is greater than that of the United States.

Arlington does not require any testing, but county officials say they are considering implementing a mandatory skin test for all new students.

Robert K. Bellam, director of tuberculosis control in Prince George's, said the county decided to recommend that foreign-born students undergo skin tests because of the increasing number of TB patients who come from abroad.

He said that of the 45 county patients reporting they had the disease last year, 17 were immigrants.

Health officials say most of those who have been exposed to TB are from the Pacific rim of Asia, from Korea in the north to the Philippines and Indochina in the south. They also say some who have been exposed to the disease come from South Asia and the Middle East.

If skin tests show that students have been exposed to the disease, health officials generally administer a chest X-ray to determine if the tuberculosis is active.

In the vast majority of cases, the disease is found to be inactive, and a year-long treatment of daily doses of antibiotics can eliminate the dormant organism.

Fairfax and Prince George's officials say they are not endorsing tests for foreign-born students who are already enrolled in the school systems because of the cost and administrative difficulties of reaching its 120,00 students.

"We do need to make changes, and that's what's happening," said Payne.

By not testing all students in the Fairfax system or all foreign-born students previously enrolled, Payne said, "we're trying to hone it down to a group we feel is more at risk."