Fairfax County students continued to score well above the national average on 1985 standardized ability and basic skills tests, according to results released by county school officials yesterday.

The overall scores were virtually unchanged from 1984 results.

Fairfax scores are now so high they may hold stable or even drop slightly in the next five years, according to Todd Endo, Fairfax schools' director of research and evaluation. Endo said he found neither possibility worrisome.

"In any one year, unless there is a dramatic change, we wouldn't pay that much attention to it," he said.

Virginia requires all fourth, eighth and 11th graders to take an ability test and skills tests in reading, mathematics and English usage that have been developed by Science Research Associates. Fairfax also tested second and sixth graders.

Test data from Falls Church also showed results that continued to be above the national average with little change. Arlington officials said they would release results today that will show improvements across the board.

Statewide results will be released June 19. Alexandria officials plan to release their results at that time.

The lowest score in Fairfax County was on the second grade reading test, in which students ranked in the 67th percentile of students nationwide. Second grade scores were the lowest in the county, but, Endo said, "They're not out of line."

Endo said county specialists are studying the second grade results, and are not yet sure what they mean. The second graders took a test different from that taken by other grades and other localities, so the results were not directly comparable. The last time second graders took the test was in 1976. Results were not immediately available.

The highest Fairfax scores were on the eighth grade math test, in the 85th percentile.

The composite scores for all three skills tests were: Second grade -- Fairfax, 71st percentile; Falls Church, 94th percentile. Fourth grade -- Fairfax, 78th percentile; Falls Church, 82nd percentile. Sixth grade -- Fairfax, 80th percentile; Falls Church, 80th percentile. Eighth grade -- Fairfax, 79th percentile; Falls Church, 79th percentile. Eleventh grade -- Fairfax, 77th percentile; Falls Church, 78th percentile.

As in 1984, about 46 percent of fourth, sixth, eighth and 11th graders in Fairfax County scored above the 80th percentile on the reading, math and language-use skills tests. The best performance was in math, in which 52 percent scored above the 80th percentile.

The percentage of students scoring below the 20th percentile on the composite skills test declined for the third consecutive year, to 6 percent of second and fourth graders, 2 percent of sixth and eighth graders, and 5 percent of 11th graders.

Staff writer Anne Koch contributed to this report