The proportion of high school juniors who still haven't passed Virginia's high school competency test has dropped to only 3 percent, state education officials reported this week. About two-thirds of those still failing are black, even though black students make up only one-fifth of the class.

Yesterday Virginia's State Board of Education decided to give the 2,305 students who haven't passed the test three more chances to take it durning their senior year.

Under state law, all students will be required to pass both the reading and mathematics parts of the 159-question test before they can graduate from high school, starting in June 1981.

This year's juniors are the first class subject to the test requirement.

When they first took the exam as 10th graders in the fall of 1978, about 18 percent failed, including almost 42 percent of the black students and 11 percent of the whites.

Since then, those who failed have been given special remedial work and two more chances at the exam -- at the end of the sophomore year and earlier this spring as juniors.

Although officials said exact figures aren't available, the failure rates now have dropped to an estimated 1.5 percent of whites and 8.5 percent of blacks.

At yesterday's state board meeting, two members, Thomas R. watkins and Henry W. Tulloch, contended those who still have not passed should be given only one more chance during their senior year. The multiple-choice exam is pegged at a ninth-grade level of difficulty, and Tulloch declared, "Repeated testing simply degrades the whole competency idea."

But a seven-member majority voted to let students take the exam three times -- a the beginning, middle, and end of their senior year. Different versions of the test would be used each time.

Board president Allix B. James said students who have made it to the 12th grade should be given every chance to obtain their diplomas.

"Somewhere along the line, the competency skills were included in the student's education," James explained. "The teacher certified the student had passed. Somebody along the line misjudged the student or misled the student. We owe that student every opportunity to show he has that bank of knowledge."

According to the new report on the test results, 1,345 blacks, 875 whites, and 85 students of other races (mostly Asians) still have not passed one or both parts of the exam.

The failure rate was considerably higher for reading than for math. This is the reverse of the pattern when the test was first given, and reflects the fact that math is more "teachable" than reading, said Gerald Bracey, director of research, evaluation and testing for the state education department.

"Some of the math skills, like adding two digit numbers are very specific," Bracey said. "But getting the main idea of a story is not something you can teach by drill and practice. It's much more abstract."