D.C. public school students scored lower on standardized achievement tests this year than they did last year, but school officials attributed the decline to the use of a new test, noting that other school systems experienced a similar drop in scores when they made such a switch.

In May, about 34,000 students in grades 3, 6, 8, 9 and 11 took the new version of the Comprehensive Tests of Basic Skills, which measures academic achievement in subjects including mathematics, reading and language.

D.C. students scored between 4 and 10 percentile points lower than last year.

The results also indicated that D.C. elementary students are at or near the national norm of school systems that use the same comprehensive test, students in grades 8 and 9 are about one year below the norm, and 11th graders are about two years below the norm.

"The dip in scores which usually accompanies a change in tests does not mean there's been a decline in achievement," said Superintendent Floretta D. McKenzie. "It means that the students are now being compared to a higher norm."

In the past the District and many other school systems gave tests that measured achievement using a standard based on student performance in 1971 -- when student achievement levels hit a low point.

With the old test, student scores increased steadily over an eight-year period from a 3.1 grade level in 1978 to a 4.1 grade level last year among third graders and from a 7.5 level to 9.4 among ninth graders.

Eleventh graders also had a steady increase since the first time the class was tested in 1981, from 8.8 to 10.2 last year.

Because the new norms, which are based on standards determined in 1981, are higher than the older ones, the District expected fewer students to score at or above the national norm.

A school-by-school breakdown of the scores will not be available until next month, school officials said.

"Considering that it's a new test, the results came out better than anticipated," McKenzie said. "I'm pleased with the teachers who helped to prevent a more serious decline."

According to school officials, about 85 percent of school systems that switch tests show a decline in student performance.

School officials for the Los Angeles Unified School District, which uses the same standardized test as the District, said student scores in that district declined after switching to the new version in 1984.

"There was a 6 to 8 {percentile} decline," said Linda Pursell, assistant director of research and evaluation for that district. "It's a common phenomenon."

Other cities, such as Oakland and Philadelphia, that use the Comprehensive Test of Basic Skills exam also reported an overall decline in scores when the new test was administered. But after the first year, the scores steadily increased, school officials said.

"We're confident we'll have an upturn from here," McKenzie said. "We see this as a baseline from which we'll go up."

The only grade that did better than last year's scores was the 11th-grade class, which had a 3 percentile point increase. But the class was also 16 percentile points, or nearly two grade levels, lower than the national norm.

The elementary school students scored at the national norm, although they had lower scores than last year. The third-grade scores were at the national norm and the sixth grade scores were only 1 percentile point below the norm.

The new test differed in organization, format and instructional emphasis, reflecting change in curricula and teaching methods of the back-to-basics movement.