Fewer than one out of every 10 Fairfax County high school 10th grade students failed Virginia's newly required minimum competency tests, according to results of the tests released yesterday by county school officials.

The tests, which the students will have to pass in order to graduate in 1981, measure basic English skills and routine matehmatical abilities such as balancing checkbooks and completing simple taxforms.

Fairfax County the largest school system in the state, said 93 percent of its 10th graders had passed the state's reading tests and 93.9 percent had passed the separate math exam.

Virginia education officials said yesterday the Fairfax scores were "running real high" and will probably be higher than the statewide results, which probably will be annuunced in mid-January.

In Falls Church, the only other Northern Virginia school jurisdiction whose results were available yesterday, a low failure rate also was recorded. Of the 124 10th grade students in the small school system who took the exams, all but 10 passed the reaeding test and all but eight passed the math test, School Superintendent Warren Page said.

Virginia State School Superintendent W. E. Campbell has said he is projecting that 85 percent of the students in the state will pass the reading test and 82 percent will pass the mathematics tests. Campbell said he is baiing his projections on test results he has received from about 25 percent of the state.

The tests are the result of a 1978 state law that requires all high school graduates after 1981 to have passed minimum competency tests in reading, mathematics, social studies and job entry skills, in addition to earning mandatory course credits.

Fairfax School Superintendent S. John Davis saie yesterday, "I had anticipated a 90 percent passing rate. With 93 and 93.9 percent, I was very pleased." The tests "measured the kinds of competency youngsters ahould have in going out into the world today," Davis said. "It's a functional type of knowledge. I call teem survival skills."

Of the 10,905 Fairfax County students who took the reading test last month, 10,142 redeived a passing score and 768 failed. There were 10,951 sutdents who took the mathematics test and 10,279 passed, 672 failed.

Students who have failed to pass the tests will have three more opportunities to take the tests before graduation, school officials said.

"I don't know if the tests are too easy," Davis said. "What might be considered a minimum competency in Fairfax may not be one in other jurisdictions," he said. Davis said he would have preferred that the state allowed each jurisdiction to devise its own minimum competency tests or let the jurisdictions expand upon the state tests by adding questions directly related to a student's study.

The State Board of Education is allowing jurisdictions to prepare their own tests in social studies and job entry skills, the other minimum competency tests. Those tests will be given in the spring.

The state allowed Arlington County schools to be exempt from the tests because, unlike Fairfax Conty, it had already development and implemented minimum competency tests in reading, mathematics, and other skills. The 1,264 Arlington 10th grade students who took the locally administered tests last spring recorded a much higher failure rate than did the Fairfax students.

According to school officials there, 72 percent of the students passed the reading test: 66 percent passed a writing test; 69.8 percent passed a math exam; and 62.8 percent passed a social studies test.

Alexandria school officials said yesterday they will release results of the state tests at a school board meeting tonight.