Third-grade students in the D.C. public schools achieved national norms on standardized tests in mathematics for the first time in more than 10 years as the school system's scores in reading and math continued to rise for the third year in a row.

The gains by the third-grade youngsters were relatively minor because they fell only one month short of the national norm in mathematics last year. But a dramatic increase was posted by ninth graders, who made the greatest gains of all students here. They improved their scores by a full year in mathematics after a number of years of achieving virtually no progress. yBut even this significant gain left them about two years behind national norms in both reading and mathematics.

The standardized tests were taken by pupils in the third, sixth, ninth and eleventh grades. With the exception of the third graders, District students remained between a half year and three years behind national norms in both subject areas. The tests were given in the spring, and marked the first time 11th grade children had participated since 1977.

Acting Superintendent James T. Guines called the gains "the best hard-nosed testimony" that the school system's three-year-old competency-based curriculum (CBC) is working. He also credited teachers and the increased involvement of parents in city school activities with helping to improve the youngsters' performances.

The CBC program was started by former Superintendent Vincent E. Reed's administration in an effort to reverse the trend of low achievement by public school students here. The program emphasizes reading and math and allows students to work at their own pace, requiring them to master one skill before moving on to another.

The fact that most students still lagged far behind the national norms, especially in reading, Guines said, "must be looked at in the context of where we were" in prior years. "We're not going to say the tests are bad or the kids can't do it," he said. "We will do better in the future."

The national norms for the various grades are 3.8, 6.8, 9.8 and 11.7. District third graders this year scored 3.5 in reading and 3.8 in mathematics, up from 3.3 in reading and 3.7 in mathematics last spring.

Since the tests are given near the end of the school year, third-grade pupils should be close to fourth grade-level work.

Sixth-grade students here scored 5.9 in reading and 6.4 in mathematics. The reading scores were up from 5.8 last year, but the mathematics scores went down from 6.5.

Ninth graders moved from 7.3 in reading last year to 7.7 this year. But the most significant gain was in mathematics where the students scored 8.0 this year, up from 7.0 last year.

School officials credited these gains to a program started this year in the junior high schools. It requires students to take extra courses in reading and math and requires their parents to sign a "contract" guaranteeing that they would check homework, provide their children with a quiet place for study and participate in parent-teacher conferences.

"It paid off," acting vice superintendent J. Weldon Greene said of the program. "They [ninth graders] went up one full year in mathematics and that's not easy to do. It shows how intensive instruction can increase performance on standardized tests."

Greene said additional reading and math courses will be required in all junior high schools next year.

The 11th grade students fell the furthest below national norms, scoring 9.1 in reading and 8.8 in mathematics. Greene said school officials thought there was a need to begin testing high school students again. High school teachers also wanted more test data on the students, Greene said.

Reading test scores dropped dramatically in grades six and nine between 1976 and 1977, but stayed fairly stable in grade three. Then, in 1978, they all began a steady rise.

Math scores dropped sharply in grade nine in 1977, but then began climbing in all three grades in 1978.

The national grade level norms are based on scores of a representative national sample of about 130,000 students tested in 1973. The norms have not been revised since then and thus do not reflect changes around the country since 1973. They do, however, provide a consistent measure of achievement in Washington.

The scores are based on a 10-month school year. The test itself is a three-hour multiple choice exam called the Comprehensive Test of Basic Skills (CTBS). Ti is published by the California Testing Bureau, a division of McGraw-Hill Inc.

"Lots of people have said these tests are biased," Guines said last night. "So this must be the acid test" that the District's program is working, he added.