The Washington area's most affluent school systems registered the highest average scores on the Scholastic Aptitude Test, according to figures released this week.

Montgomery County led the region with an average overall SAT score of 989, followed by Fairfax County with 976, Howard County with 963 and Arlington County with 952.

Of the area's eight major public school systems, the District scores are the lowest at 707 points -- almost 200 points behind the national average -- followed by Prince George's County with an average overall score of 809. The District's overall average, which includes private school students, is 850.

The Prince George's scores represent a continuing decline, despite efforts to bolster student performance, particularly among minorities.

"We're not pleased with the fact that we have not responded in a more positive direction," Prince George's Superintendent John A. Murphy said yesterday.

Murphy said the county should soon see the long-range benefits of changes in the elementary school curriculum and teaching methods made five years ago as those students who have benefited from the changes move into high school. Murphy said he expects to see improved SAT scores in coming years.

The local school systems' scores parallel slumps throughout Virginia and Maryland. Nationally, the reading scores for the more than 1 million students who annually take the college entrance exams fell three points from the previous year, continuing a long-term trend. Math scores have held steady.

Reflecting that trend, Montgomery County's math scores increased by a single point to 526 over last year's scores, while verbal scores fell by four points to 463 -- the worst performance since 1984.

Educators say the results highlight the fact that students are reading less and watching television and music videos more -- at least three hours daily, according to a current national study. "Maybe we ought to give a video SAT," said Arlington schools spokesman David Rorick.

Except for the District and Prince George's, local scores are well above the national average of 900 -- 476 for math and 424 for verbal -- out of a possible combined score of 1600.

The SAT exams are used primarily as an indicator of a student's ability to succeed in college and are an admissions requirement at many colleges and universities. Local officials note that more of the area's graduating seniors take the voluntary exam than students in other parts of the country.

A higher percentage of students taking the test increases the chances that average or below-average students will pull down scores, according to testing experts.

In most jurisdictions, Asian students continued to outscore other ethnic groups in math. Whites had the highest averages overall, while black students lagged behind.

Anne Arundel County students' average overall score of 907 represents a 13-point drop over the previous school year, but keeps them just above the national average.

Alexandria scores dipped by two points over the previous year to a combined score of 926, representing a seven-point decline in verbal scores and a five-point increase in math.

In Arlington, overall scores fell 12 points to 952. Math scores were relatively steady at 507 points, but verbal skills dropped 11 points to 445.

The Howard County composite score for 1990 was 963, three points higher than last year. The verbal score was 452, down two points from last year. Math was 511, five points higher than last year.

In Montgomery County, the average SAT score of the 4,800 students who took the test dropped by three points from the previous year, but remained 89 points above the national average.

In Fairfax County, math scores dropped by one point while verbal scores fell by six points.

Scores for Prince William and Loudoun counties were unavailable.

Staff writers Michele L. Norris, Amy Goldstein and Claudia Levy contributed to this report.