The reading competence of seventh graders in Prince George's County increased by six percentage points in 1977, but still remained slightly below the statewide average, according to test results released yesterday.

The results showed that 70 percent of the county's public school seventh graders achieved "competent" scores on the Maryland Functional Reading Test last fall, as opposed to 64 percent in the fall of 1976. The statewide average for 1977 was 72 percent.

The county's 11th graders, however, made no improvement over that period. The test results showed that 86 percent of the students at that grade level earned competent scores in both 1976 and 1977. The 1977 statewide average for 11th graders was 89 percent.

The test was given to Prince George's ninth-grade students for the first time last fall. While the statewide average for ninth-graders was 74 percent, only 72 percent of the Prince George's students earned competent scores.

The tests have been administered throughout the state since 1975 as part of he Maryland Accountability Program. A student must correctly answer at least 80 percent of the test questions to be considered competent in reading skills.

School superintendent Edward J. Feeney said he was encouraged by the Prince George's results, particularly at the seventh-grade level. He attributed the gain there to new reading materials and exercises that were introduced into the classrooms in 1976.

"We are now expanding our efforts," said Feeney. "I believe we can show the same kind of progress at the upper grade levels."