For the third straight year, Prince George's County 10th grade students scored near the national averages on a standardized test of reading, language and math skills, according to test results released yesterday.

School officials took the results as a sign that performance in the school system remains steady despite severe budget cutbacks over the last few years.

"It demonstrates that academics will not be sacrificed despite our financial situation," said school spokesman Brian J. Porter. "We're holding our own, even with our diverse student body."

The approximately 140-minute-long test, called the Comprehensive Test of Basic Skills, was given to some 8,000 10th graders last April over a period of three days. The multiple-choice exam covered a wide range of skills including vocabulary, reading comprehension, language mechanics, spelling and math computations.

The county began giving the test in 1977 after the school board called for a program of proficiency testing, "to ensure that Prince George's County students know how to read, write and perform computations adequately before they graduate," according to a board resolution. Prince George's is the only jurisdiction in Maryland that administers the test.

A comparison of 1982 to 1983 results showed a slight improvement of two school months in reading comprehension and math computation, from 10.0 to 10.2 and 10.6 to 10.8, respectively.

"It means that about one student in seven answered one more item correctly on the test," said Elwood Loh, testing chief for the schools. "Since we started giving the test in 1977 the scores have basically stayed the same," Loh said. "We use the test to get a handle on how the kids are doing at the 10th grade level."

Overall improvement in test performance was shown at 11 of the county's 20 high schools. One of the largest improvements was at Bladensburg High School, where the total reading score improved from 8.8 to 9.6, a jump of nearly a year, although performance remained below the national average.

"It certainly doesn't mean we've achieved all our goals," said Porter, but "the superintendent and those board members who have reviewed the test results are very pleased."