A greater percentage of black students in Arlington public schools failed minimum competency tests designed to measure basic skills in reading and mathematics than students in any other group.

That conclusion is contained in a report on results of pilot minimum competency tests given ninth graders last spring.

By 1981, all high school seniors must pass state math and reading competency tests in order to graduate from high school in Virginia.

According to the report, which was to be presented to the school board last night, 28.5 percent of all Arlington ninth graders failed the minimum competency reading test, which asked students to answer questions based on a sample paragraph. Failure rates were as follows: 55 percent of the black students who took the test failed, as compared to 35 percent of the Hispanics, 33 percent of Asians and 19 percent of whites.

On the math tests, which 30 percent of all ninth graders failed, 62 percent of the black student who took the test failed it, as compared to 29 percent of Hispanic, 22 percent of white and 19 percent of Asian students. Typically, this test asked students to figure sales tax and balance a check book.

School Superintendent Larry Cuban said he was surprised by the results.

"Academically, achievement in Arlington has been mostly stable," he noted at a press conference. "The system still scores above the state averages and national norms. Nationally, the pattern is that minority youngsters don't do as well on tests as white kids. Until now, we had no data whatsoever about Arlington. When we saw large numbers of blacks failing minimum comptency tests in Arlington . . . that surprised me.

School Board member Thomas Penn said: "I'm very concerned about these results. They tell us what many people in the (black) community have been telling me all the time, which is that the system has not been satisfying the needs of the black students."

Penn said that some black parents have complained to him that their children are ignored in class and that high school students were spending more time in the halls than in class. "Once we find out what the problem is, I'd like to see more involvement by parents," he said.

More than a third of Arlington's 16,000 students are nonwhite. Blacks account for about 15 percent of all students. Asians for 8 percent, Hispanics for 6 percent and other minorities for 5 percent.

Board Chairman Mary Margaret Whipple noted at the press conference that since 1974, as school enrollment has steadily declined, the number of students whose native language is not English has jumped from 7 to 19 percent. Students with fewer than two years instruction in English did not take the tests.

In addition to the ninth graders' results, combined results for fourth and sixth graders on standardized reading tests show that of those reading two or more years below grade level, 41 percent were whites, 34 percent blacks, 17 percent Asians and 7 percent Hispanics. The report did not say what percentage of each group failed these tests.

Cuban made several recommendations, among them that course content be reviewed to ensure that basic skills are taught and that an individual plan be devised for each low-scoring student needing remedial efforts.

This year Arlington opened basic skills centers in every school for children who need remedial help. In response to substantial parental demand, Arlington also opened a traditional elementary school that emphasizes basic methods of education, including textbook instruction and self-contained classrooms.