Black students in Montgomery County public schools scored slightly higher than they did last year on aptitude and achievement tests administered last March, narrowing the difference between their marks and white students' scores, county school officials said this week.

Steven M. Frankel, director of the Department of Educational accountability, said the results could not show "definitively" that black students' skills had improved because only two years of tests were compared. But he claimed that the scores showed that blacks and the school system were "moving in the proper direction."

the scores of both blacks and whites improved, but blacks' test scores narrowed the gap between the two groups by one to three percentile points. During both years of testing, white students scored above the national mean on such tests, while black students scored below it. The national mean on such tests is 50, but the average Montgomery County student last year performed better than two-thirds of the students in the nationwide group.

Asian students scored higher than white students for the past two years, and Hispanic students' scores were lower than white students' but on a par with the national average.

Frankel said he could not give an overall percentile rating for each racial group; he could only compare racial groups' test scores according to years in school.

For example, in the Iowa tests of basic skills - which measures vocabulary, reading comprehension, language usage, map reading and mathematics problem solving - county black students in the seventh grade achieved an average percentile score of 26, meaning they scored better than 26 percent of students in a national sample. But county white students in the seventh grade achieved an average percentile score of 63, or 37 points higher than black students.

Last year, the difference between percentiles scored by white students and black students in the seventh grade was even larger - 55 points.

School officials said they did not know of national studies of black students that used the same factors as the Montgomery County study.

Superintendent Charles M. Bernardo said the test results were interpreted according to racial groups in response to charges by the Black Relations Monitoring Committee several years ago that the school system was not meeting the educational needs of blacks.

Bernardo said that as a result of the differences in test scores between white and minority groups, extra teachers would give remedial help to minority students, more minority teachers would be hired, and basic language and mathematics skills would be stressed in the classrooms.

"The gap (in scores) is not a function of race," Bernardo said. "It's a function of socioeconomic backgrounds. One's racial or ethnic derivation is not a determinant of one's potential to do well."

Bernardo also released test scores on the 1978 Scholastic Aptitude Test (SAT), or college board exam, showing that Montgomery County public high school seniors scored 36 points above the national average on the math section.

The national verbal SAT score was 429 (on a scale of 200 to 800) and the national math SAT score was 468.