Alexandria's T.C. Williams High School has 18 semifinalists this year for the prestigious National Merit Scholarships, more than any other school in Virginia.

The achievement was announced last night at a public meeting of an Alexandria task force studying plans to provide health services to students.

Reached later by phone, T.C. Williams Principal John Porter said 18 students had earned the title this year, compared with seven last year. A school official said McLean High School in Fairfax County ranked second, with 13 semifinalists. The scores are to be released officially next week.

Porter attributed his school's success to the hard work of students, staff and their families. "I feel really good, very, very pleased with the results," he said.

He said that, in line with a nationwide trend, T.C. Williams has emphasized test-taking skills. But he added, "I think most of the credit goes to the kids and the things they received at home."

T.C. Williams, Alexandria's only high school, has an enrollment of about 2,200. Its student body is one of the most economically and racially diverse in the Washington area.

Alexandria School Board Chairman Timothy Elliott said he had "guarded optimism," noting that two years ago the school produced 15 semifinalists, then had fewer than half that number last year. "I hope it's not a cyclical thing," he said. "I would like to see a high number continue for a couple of years."

Langley High School in Fairfax County had the largest number of semifinalists in Virginia last year, 28. This year, 10 Langley students are semifinalists.

Semifinalists are chosen on the basis of scores on the preliminary scholastic aptitude tests, which students took last year when they were juniors.

Finalists -- those who win scholarships -- are chosen according to a combination of test scores, leadership ability, contributions to their school and community and recommendations from the school.

This year, 13 Northern Virginia scholars of 2,800 nationwide won scholarships worth from $1,000 to $8,000 for four years of undergraduate study.

The scholarships are awarded by the National Merit Scholarship Corp., which has been conducting the competition since 1955.