A recently arrived Pakistani teenager has been found to be suffering from tuberculosis, prompting mass tests of all 600 other students at his Northern Virginia school for traces of the dangerous disease.

The youth, who recently began attending Kenmore Junior High in South Arlington, is currently quarantined in his home and will not be allowed to return to the school until he is not contagious, school officials said yesterday. His case is believed to be at least the fourth case of active TB confirmed in Washington suburban schools in the last two years.

The mass testing at Kenmore, located on Carlin Spring Road near Rte. 50, is the first such program of its kind in the Virginia suburbs. Test performed on Kenmore faculty members last week failed to find any traces of the disease.

Although tuberculosis has been largely eradicated among native-born Americans, it remains common in Asian countries, officials at the federal Center for Disease Control said yesterday. In Arlington, where the latest case was found, officials conduct a regular TB prevention program in the schools, where nearly one out of every 10 students is an Asian.

That ratio is higher at Kenmore where nearly one out of every four students is a new arrival to the U.S., mostly from Asian and Latin American countries.

TB cases are considered even more rare in the suburbs than in cities.

Health officials said they believe there is no reason for Arlington parents to be overly concerned. "Tuberculosis is not a highly communicable disease," said Dr. Kenneth Powell, an official of the federal disease center's tuberculosis control division.

The disease typically thrives in large families and in crowded housing areas. It is caused by a bacteria that settles in a person's lungs.

The bacteria can live for years without, causing symptoms but at other times the disease can flare into an active case, causing a cough that can spread disease to others and an infection that can attack other organs.

A person with active TB has a fever, loses weight and feels rundown. Early, inactive TB usually is not evident even on a chest X-ray and must be diagnosed by a special skin test.

Virginia law requires that all incoming students -- including new arrivals from other countries -- be immunized against polio, diptheria, tetanus and measles. Public health officials in each jurisdiction are attempting to screen new immigrants for TB, but they say their efforts are frustrated because newly arrived persons often are hard to locate.

Last fall active TB was discovered among two newly arrive Indochinese high school students in Montgomery County.

"We didn't panic but some parents did," said Dr. Harold I. Passes, the county's chief of public health. Passes said that students and staff who came into close contact with the students received skin tests to determine whether they had contracted the disease. No other active cases were discovered, Passes said.

'We didn't do mass testings because if we did that we'd be doing nothing else," said Passes. He said he believed a mass testing program such as Arlington's was "a sheer waste of time."

Patricia Wireman, an Arlington school nurse, defended the mass testing program. "Maybe we're just stricter than other places, but who's to say who this student came in contact with?" she said.