Standardized test scores for Loudoun County students vary slightly from last year's results and remain well above the national average, according to data recently released by school personnel.

Similar variations were noted in 1986-87 scores for students in Manassas, which also scored above the national norm, while in adjacent Manassas Park some composite scores fell below the 50th percentile.

Virginia requires that all fourth-, eighth- and 11th-grade students take standardized tests in reading, math and English usage. Manassas administers the tests, developed by Science Research Associates, to grades one through six, eight and 11. Manassas Park tests students in kindergarten through 11th grade, while Loudoun County tests grades two through 11.

Overall, Loudoun County students are generally keeping pace with their counterparts from a year ago, according to the test results.

"Our scores are basically competitive with last year's," said Gordon Fletcher, planning director for the 13,000-student, 900-teacher Loudoun school system. "We look for growth, but the main thing is to make sure that there are not significant changes downward. We are pleased with how our youngsters are progressing."

Composite scores, combining math, reading and language arts, in Loudoun continued to exceed the national norm, ranging from the 70th percentile for this year's eighth graders to the 80th percentile for second graders. In four of the 10 tested grade levels, composite scores were higher than they were last year; four levels were lower, and two remained the same.

Fourth graders scored in the 74th percentile, down 2 percentile points from last year, but better than 74 percent of all the students taking the tests nationwide. Eighth- and 11th-grade students scored in the 70th and 74th percentiles, down 4 and 2 points, respectively.

In Manassas schools, composite scores in five of the eight tested grade levels were higher than they were last year, with two lower and one unchanged.

Test results for the city's school system, which has 4,100 students and 345 teachers, had composite scores ranging from the 64th percentile (11th graders) to the 82nd percentile (second graders). Fourth graders scored in the 73rd percentile, a one-percentile-point drop from last year. Eighth- and 11th grade students scored in the 65th and 64th percentiles, respectively, compared with 62nd and 73rd last year.

In Manassas Park, a small school system with 1,400 students and 100 teachers, five of the 11 grade levels tested higher in composite scores, five scored lower and one remained unchanged.

Composite scores ranged from the 35th percentile for 10th graders to the 73rd percentile for fifth graders, according to results provided by Jeannette Pillsbury, assistant superintendent for instruction.

Jimmy Stuart, superintendent for Manassas Park schools, said that overall he was pleased with student progress on the tests over five years, but noted there was concern about sizable drops in the fourth- and eighth-grade composite scores.

Manassas Park fourth graders scored in the 49th percentile this year, compared with the 61st percentile last year.

Composite scores for eighth graders dropped from the 58th percentile last year to the 48th percentile this year.