Children entering the Arlington school system will have to undergo a skin test to determine whether they have been exposed to tuberculosis, the county School Board decided last night.

The board voted unanimously to require new students to present the results of a tuberculin skin test within one year of entering school. The requirement goes into effect immediately, but will not affect students already in school.

Previously, the school system recommended that students be tested but did not require it. All school employes must receive a skin test for TB every three years.

Fairfax and Prince George's counties recently began procedures for screening foreign-born students for TB, citing figures showing a higher incidence of exposure to the disease among foreign-born students than among those born in the United States.

Arlington school officials cited similar reasons for their change in policy. "We're getting a lot more immigrants who may have been exposed to TB, and better safe than sorry," said School Board Chairman Gail H. Nuckols.

Fairfax began this year to require foreign-born students entering public schools to undergo a TB skin test, and Prince George's school authorities began to urge new foreign-born students to be tested.

District of Columbia and Alexandria schools require all entering students to be tested for exposure to the disease. Montgomery County began three years ago to require tests for foreign students from countries whose rate of TB is greater than that of the United States.

Tuberculosis, a contagious disease that can destroy the respiratory system, can be controlled with antibiotics. In the last 30 years there have been nine cases of TB among Arlington students and staff, school officials said.