The D.C. School Board last night adopted a plan requiring all public elementary school students to demonstrate adequate skills in reading and mathematics before moving up to the next grade.

The competency plan, approved on a 10-to-1 vote, marks the first time the school system has established specific standards for the promotion of students. The board in 1977 banned "social promotions" -- passing failing students on to the next grade simply because of their age -- but teachers still have in most instances automatically promoted students to junior high school once they have reached age 13.

The new policy will take effect next fall in grades one through three. The next year it will be the rule for all elementary grades.

The plan provides a checklist for teachers of the skills students must master in reading and math in each grade level before moving on. For example, a sixth grader must be able to compute percentages, divide by decimals, multiply sets of four-figure numbers, describe mood and character traits and plots in literary works and identify metaphors, hyperbole and personification.

In addition, the new plan calls for student promotions on a half-year schedule. Passing students, for example, will move from grade 6a to 6b at the half-year point. Students who are having difficulty in both reading and math will be kept at the 6a level and receive special attention and remedial help, according to Dr. James T. Guines, associate superintendent for instruction.

Some students who are weak in only one of the two main subject areas will be placed in "transitional grades," Guines said.

In some schools, students at all levels will be taught in the same class, but teachers will be required to give them help according to their individual needs. In other schools, students on different levels will be in separate classes.

Guines said he did not yet know if the plan will require more teachers in the system. "We will know better after the first year," he said.

This could cause a difficult problem for the success of the plan because of ever-tightening budget constraints. Superintendent Vincent E. Reed has recommended eliminating about 700 teaching positions in the next school year.

Frank Smith Jr., the only board member opposing the plan, said he thought it "will result in most of our minority students being pushed out of school. I have this image of my 8-year-old daughter in the third grade sitting in class with some 15-year-old who hasn't passed math. Holding that kid back is not going to help my 8-year-old who's progressing along.

The plan also calls for more frequent parent-teacher consultations on the progress of each student.

Students will continue to receive the prescriptive reading and math tests as well as the competency tests of basic skills. These tests will merely be a backup to make certain the teacher's assessment on each student's skills has been correct.

The plan is part of the school system's efforts to improve the generally low performance level of public school students. D.C. students have consistently scored lower than their counterparts in other local jurisdictions and below national norms in reading and mathematics. Some students graduated from the city high schools without being able to read.