Continuing a pattern of academic progress, Prince George's County student scores on one of the major standardized tests have taken their biggest one-year jump, according to figures released yesterday.

At the same time, black students, whose scores have lagged behind others, earned their highest scores ever, surpassing the 60th percentile.

The results of the California Achievement Test, administered last fall, show a continuation of the academic gains that have been made in the area's second largest school system since 1982. During that time, the greatest gains have been in the elementary levels, with average scores for third graders climbing 23 points.

"You can see the shift from an average system to an excellent system dramatically taking place," Superintendent John A. Murphy said at a news conference announcing the results. He cited higher teacher salaries, training for principals, higher expectations for students and smaller classes as factors.

Three years ago, Murphy set a 1990 goal of having Prince George's students break into the 75th percentile. That goal was bolstered by third graders whose scores last fall reached the 73rd percentile, a jump of 8 points from a year earlier and the highest level ever posted by any grade in the county.

Fifth graders' scores increased 7 points, to reach the 69th percentile. Eighth graders scored at the 67th percentile, a 3-point rise.

The county is in the third year of a court-ordered desegregation plan, but officials said the specialized magnet or compensatory programs are not solely responsible for the overall achievement.

"It's {the result of} a whole process," school board member Catherine M. Burch said.

The exam is given to third, fifth and eighth graders and, in alternate years, 11th graders. The test, known as the CAT, is a general measure of learning in reading, mathematics, spelling and language.

Murphy has predicted that by 1990 scores will be significantly above the 75th percentile. Such a score would place the system among the top 25 percent in the nation, with 75 percent of all students nationwide scoring below. The national mean is the 50th percentile, with half the students scoring below and half scoring above that level.

The CAT is required in all Maryland schools. Other area school systems have not yet reported the results of standardized tests. Last year, Montgomery County students scored at the 80th percentile. Students in the District and Fairfax are given other standardized tests.

Across the country, black and minority youngsters have not performed as well as white students on standardized tests. In Prince George's, the gap between the average scores of black and white students has narrowed since 1984, the first year results were analyzed by race, primarily because of gains by black youngsters.

For example, the gap was 25 points among third graders in 1984 but was 17 points in the most recent tests. During the same period, the gap among fifth graders dropped from 25 points to 20 points and among eighth graders from 24 to 22 points.

Still, black eighth graders posted the lowest overall scores, at the 58th percentile, 12 points higher than in 1984 but still well below the 80th percentile scored by white eighth graders this year.

Closing that gap has been a major goal in the county, where 62 percent of the 103,000 students are black. Board of Education Chairman Barbara Martin said yesterday the scores of black students are not disappointing.

"When you put it all in context, you'll understand they've come far. The gap isn't widening," she said. Selected School Districts

SCHOOL SYSTEM...ENROLLMENT...SALARY

Baltimore.........110,189...$88,000

Boston.............67,000....95,000

Cleveland..........72,639....90,000

Dallas............131,473...125,000

Denver.............59,423....78,629

Indianapolis.......50,437....88,029

Memphis...........107,019....75,000

Milwaukee..........96,000....80,000

New Orleans........83,000....96,000

San Francisco......65,558....95,000

St. Louis..........46,636....94,500

Area School Districts:

Alexandria..........9,490....$85,000

Arlington..........14,307.....80,000

District...........87,000.....85,000

Fairfax County...128,592.....100,000

Loudoun County.....13,562.....75,000

Montgomery County..96,271.....96,000

Pr. George's County..103,000..95,925

Pr. William County...39,106...82,000