D.C. public school scores on national achievement tests either dropped slightly or did not improve in most grades this year, halting the widespread progress that students showed on the tests last year.

Scores among elementary school students slipped in reading, math and language, but for the most part remained above the national median. In junior high grades, minor gains and declines were recorded. And high school students either improved a bit or held the ground they reached last year.

Although clearly unenthusiastic about the scores, school officials said yesterday they were not disheartened. "I wanted a higher level of achievement than we had last year, but I'm not frustrated," said School Superintendent Andrew E. Jenkins. "To improve takes hard work over time. We still have a way to go."

Jenkins, who has been under fire from school board members for his performance, said he has begun a review of all instruction programs. A team of aides has been given two weeks to assess common problems that affect student work, then propose solutions, he said.

The annual achievement tests are only one of many instruments used to evaluate students, but the results have become a gauge of how well the city's classrooms are working. Last summer, at a jubilant ceremony, Jenkins described student strides on the national test as a significant sign of progress.

There has been no such celebration this time. The performance of high school students was reassuring, officials said, but steady climbs upward in elementary and junior high grades had been anticipated.

Schools had been asked to spend more time preparing for the tests, which are given in May to students in third, sixth, eighth, ninth, 10th and 11th grades. Jenkins created an office whose only purpose is to improve test scores. Last fall, he shipped six dozen administrators back to local schools to assist teachers with instruction.

"With all of these initiatives, I was expecting to see another spurt upward," said school board member Wilma R. Harvey (Ward 1). "It's disappointing. What bothers me is that we look stagnant."

Board members also had hoped to see the scores rise because this year was the fourth time that D.C. students were evaluated using relatively new national standards and tests.

In the early 1980s, District test scores rose routinely until the system began using a new version of the Comprehensive Test of Basic Skills. The switch led to steep declines in scores -- a common occurrence for school districts that make such a change. Ever since, D.C. scores have defied prediction.

They did not budge in 1988. They crept up in nearly all categories last year. Now, with the slight drops in many areas, school officials and parent activists are hesitant to predict what's wrong or what's next.

"I don't think losing a few points is statistically significant," said Bettie Benjamin, president of the D.C. Congress of Parents and Teachers. "If they continue to drop over the long haul, then I will be much more concerned." School board member Erika Landberg (Ward 3) said she fears that too much alarm over this year's results will pressure schools to shelve other lessons and instead "teach to the test" in pursuit of better scores.

"I don't think this is cause for apprehension," Landberg said. "It is cause for us to do a better job than we're doing now."

Landberg and other officials said they were pleased with high school students' scores. The District's high schools have long been a critical problem. School system leaders estimate that four of every 10 high school students quit before graduation, and among those who stay, the cumulative grade-point average is 1.8 on a four-point scale.

High school scores remain below the national median, but are moving forward. Reading scores for 11th-graders are now at the 40th percentile. Two years ago, they were at the 30th percentile. Math scores are five points higher than two years ago, and language scores are six points higher.

Elementary and junior high grades showed a different picture. While eighth- and ninth-graders fared almost the same as they did last year, elementary students fell a bit in all categories. That's unusual; in previous years, those students have fared best on national tests.

The scores are the school system's second dose of unpleasant news about student achievement since May, when college placement exam results were announced. The average score of D.C. public school students on the Scholastic Aptitude Test dropped two points, to 713, the same score recorded in 1987.