Nearly three out of four Prince George's County ninth graders failed a state-mandated minimum math competency test, school officials announced yesterday.

County school Superintendent Edward J. Feeney, reacting to the report that only 26.7 percent of the students passed the multiple-choice exam, immediately announced a program for next fall that is designed to beef up math instruction and teacher preparation for the test.

The Maryland Board of Education formally voted Wednesday to make passage of such a test a requirement for high school graduation beginning in 1987. A mandatory reading test went into effect last year and similar tests also will be required in writing and citizenship.

"It is not sufficient for us to blame anyone, or to point a finger at the curriculum, the teachers or the students," Feeney said. "We all share in this poor performance. Our first responsibility now is to move forward and implement the changes to improve the scores for next year."

State school officials said the Prince George's math results were the fourth worst among the state's 24 school districts. Only Baltimore City, where 83 percent failed, and two rural counties did worse.

Statewide, only 39 percent of 50,000 Maryland ninth graders tested passed the sample Maryland Functional Mathematics test, which was given on a trial basis last fall. School officials in Baltimore City called the passing grade of 80 percent "unrealistic." In Montgomery County, whose students traditionally rank among the nation's highest on standardized tests, school officials questioned why only 65 percent of their students passed.

State School Board President Joanne T. Goldsmith, who lives in Prince George's County, predicted that scores will improve when the results count. She said students did poorly on the reading test when it was first administered in 1977 but this year, when passage was required for graduation, 80.6 percent of the state's ninth graders and 98.9 percent of the seniors passed it.

"I think you'll see a tremendous change on the math test next year," Goldsmith said.

Beginning this fall, ninth graders who pass the test will not be required to take it again. Those who fail it, and the other tests, will be offered remedial help and must retake the tests, in grades 10, 11 or 12, until they pass.

While Feeney and other Prince George's school officials said they were stunned by the results, they chose not to blame the test.

Edward Loh, chief of testing for the county schools, said some students may not have taken the test seriously because it does not yet count toward graduation. But he added, "there may be a problem with math learning" in the school system.

"It may change the way we teach it math , the demand for mastery and the intensity," said Louise Waynant, coordinating supervisor of the instruction.

"We're taking it on the chin on this one, we're not pointing the finger," said school spokesman Brian J. Porter. "The problem is not with the test. We believe students shoud have been prepared enough to pass this test."

Porter said only 45 percent of county's graduates go to college, so many need extra motivation to achieve in school.

"To the youth who aspires to work in a fast-food store, what sense is there in them caring about math--unless we tell them to," Porter said.

School officials announced the following steps to improve test scores:

* An increase in the time of math instruction in elementary school by 15 minutes a day, from the present weekly minimum of 200 minutes to 275 minutes.

* For the first seven weeks next fall, ninth-grade general math teachers will teach only from new materials being prepared to cover the seven content areas measured by the test. Forty percent of the county's ninth graders take general math, as opposed to algebra.

* A special computer program, drilling students in functional math skills, will be made available to students for use on small computers located in each high school.

* An increase in training sessions for ninth-grade math teachers, with special training for the estimated 12-14 percent who are not certified in the field, but teach math because of a shortage of qualified math teachers.

The math test was given to 9,093 ninth graders last fall. The untimed 99-question quiz was designed to be completed in 90 minutes, although some Prince George's students labored for as long as three hours, according to Porter. It covered addition of whole numbers, simple division, operations with mixed numbers and problem solving.

"I took the test, and there were a couple of times when I didn't get the answer I was supposed to," said instruction supervisor Waynant, who pointed out that the long exam was as much an exercise in math concentration as computation and concept. "We had some students who just got very weary and said 'I'm not going to finish it.' " Waynant said.

Loh pointed out that the passing grade of 80 percent was higher than the 60 percent standard required for passing the Maryland Functional Reading Test, which is already required for graduation.

Paul Williams, who heads the testing and evaluation program for the state Department of Education, said the 80 percent standard was chosen after interviews and surveys with more than 2,500 Maryland students, parents, teachers and school administrators who were shown samples of the test. Williams said both the state and the public knew that most ninth graders would fail the test on its trial run.