Prince George's County elementary and middle school students continued a five-year improvement -- scoring above the national average -- in all subject areas on a battery of California Achievement Tests, according to results released yesterday.

On a separate exam, county ninth graders also performed well on a state-required "functional" reading test, with a passing rate of 90.8 percent, which was down slightly from last year's 91.7 percent.

The best news for school officials was in the subject of language arts, where students scored from nine to 11 percentage points higher on the achievement tests than their counterparts in 1980.

While school officials said they were pleased with the achievement and reading test scores, they acknowledged they were less than satisfied with the results on two other functional tests in mathematics and citizenship.

Only 38 percent of last year's ninth graders passed the citizenship test, which was given for the first time. That test, however, will not be a graduation requirement until 1988, the year current ninth graders graduate. On the mathematics test, which becomes a graduation requirement in 1987, 52.3 percent of this year's ninth grade passed. That compares with 54 percent of last year's ninth-grade class.

"The results are a remarkable compliment to teachers," said Superintendent John A. Murphy, citing the financial constraints on the school system. He said the county has the highest ratio of students per teacher in the state and is second lowest in expenditures per pupil for instructional materials.

"If we could just untie the hands of our teachers" by lowering class size and supplying the necessary materials, Murphy said, " . . . I'm confident our system would move to a position of excellence in the Washington metropolitan area."

On the California Achievement Tests, the county improved from an overall average at the national norm four years ago to six to eight percentile points above that this year. The improvement was welcomed by officials in the system, which last week reported that 39 percent of its students had not maintained a C average.

The improvement in test scores also can be attributed to more emphasis on basic skills, according to Louise F. Waynant, assistant superintendent for instruction. She said the instructional program recently has become more structured and consistent throughout the system.

Although the worst performance for the county was on the citizenship test, officials said the results matched the statewide average.

Testing Director Elwood Loh said the citizenship test is "very difficult" and "students are required to remember very heavy questions." Students, for example, are asked to distinguish between the powers of state and federal governments and various levels of the state court system.

Students can take the citizenship and other functional tests several times before graduation.

The achievement and functional test scores once more showed weakness among county students in problem solving and comprehension skills, according to Waynant. She said several steps will be taken, including more frequent testing and computer-assisted instruction in math and new summer school programs on the math and civics skills.

In addition to remedial programs, improved results will depend on increased funding, Murphy said. While the Board of Education has requested $362 million for fiscal 1986, County Executive Parris Glendening has indicated that he will be forced to cut that by about $14 million.

The California tests were given to third, fifth and eighth graders last fall. Third graders have, since 1980, improved their percentile rankings from 44 to 54 in reading, 53 to 64 in language and 47 to 60 in math.

Fifth graders, over the same time period, have brought their percentiles from 47 to 53 in reading, 53 to 64 in language and 47 to 58 in math. Eighth graders have improved from 48 to 52 in reading, 52 to 61 in language and 53 to 56 in math.

On the functional reading test, 99.7 percent of this year's high school seniors have passed. On the math test, 73.9 percent of the county's 10th graders have passed.