Fairfax County black students scored at or above the national norm in overall achievement on standardized tests for the first time this year, but continue to lag far behind white students in every grade level, test results showed yesterday.

"It's proof that the system is working," said Superintendent Robert R. Spillane, who scheduled a news conference today to announce the results. Spillane said the school system now will seek to identify "promising practices" that have helped to increase scores at individual schools.

"We have a way to go but we're heading in the right direction," said School Board member Olivia Michener.

The results, obtained yesterday by The Washington Post, showed that black students made the biggest score gains of all ethnic groups since 1983.

Despite the increase, stubborn gaps remain between black and white students. In 11th-grade reading, for example, blacks scored 33 percentile points behind whites, unchanged from 1985 but smaller than the 42-point disparity in 1983.

They showed that while white students' overall scores were at least in the 82nd percentile -- equal to or higher than 82 percent of the students across the nation who took the test -- black students' overall scores ranged from the 50th percentile to the 59th.

Hispanic students scored higher than blacks, ranging from the 63rd to 71st percentile in overall achievement, but lower than whites. Asian students outscored whites in math, and were about equal in overall achievement.

The results are embarrassing for a county that prides itself on its school system and one in which minorities constitute a growing percentage of the school population. One in five Fairfax students is from a minority group; 9 percent are black.

The Fairfax results echo those of other area jurisdictions that have begun efforts to erase the black-white score disparity. Alexandria officials announced this month that all elementary pupils had scored above the national norm last year.

The Fairfax scores showed results for fourth, sixth, eighth and 11th graders on the Science Research Associates achievement tests administered by the school system in reading, math, language skills and overall achievement. Scores are calculated based on performance of students across the nation who took the test in 1976; because national scores have risen in recent years, Fairfax student scores may appear higher than they actually are.

Fairfax County also compiled scores by ethnic group on the Stanford Achievement Test for second graders. The results showed a 24-point gap between black and white pupils on the test, although black scores generally were higher in second grade than in higher grades.

Despite Spillane's optimistic view, the president of the Fairfax County Federation of Teachers, Rick Nelson, said the results continue to show that scores for minority students, unlike whites, fall in secondary schools. Nelson blamed the problem on tracking of minorities into less challenging classes.

Spillane, however, said the problem stems partly from the higher mobility of minority students, who are more likely than whites to receive early education in another school system.

He said the school system will undertake a study trying to link the number of years a student spends in the county to improvements in scores.