Arlington County school officials said 99.5 percent of last year's seniors passed the state-required competency test for graduation.

Last year was the first time students were required to pass the test, which covers fundamental skills in reading and mathematics, such as how to balance a checkbook or read a recipe. The once-required social studies test for Arlington students was dropped in favor of required courses in American and Virginian history and government.

The competency tests are administered in the sophomore and junior years. Students who do not pass the tests in either of those years are given three chances to pass during their senior year. Those who still fail the test are denied a regular diploma, but may take the tests again after their senior year.

Already, 94.6 percent of last year's juniors have passed the reading and math tests, while 88.4 percent of last year's sophomores have successfully completed the tests.

Handicapped students are given special diplomas for meeting competency tests specifically designed for them. In the Class of '81, 93.3 percent of the handicapped students passed their tests.

At Yorktown and H.B. Woodlawn high schools, 100 percent of last year's nonhandicapped seniors passed the tests. At Wakefield High, 99.7 percent completed them successfully and at Washington-Lee, the figure was 99.4 percent.

Overall, blacks, other minorities and white students who were seniors last year performed comparably on the tests. Among last year's juniors, 93 percent of the black students and 97.5 percent of the whites have passed both tests, while only 79.6 percent of those in other minority groups -- mostly Hispanics and Asians -- passed.

For last year's sophomores, 92.3 percent of the white students have passed, compared with 74.4 percent of the blacks and 80.5 percent of those in other minority groups.