Paul Masem made his first major policy initiative as Alexandria's school superintendent by asking School Board members last night to shift the focus of its minority achievement program to those students scoring at the bottom third on national standardized tests.

In a briefing paper, Masem proposed targeting specific students rather than trying to narrow the academic gap between all minority and white students, which has been the board's policy up to now.

There are 773 high school students who would qualify for the program, school officials said. The number of junior high and elementary students has not been determined.

The proposal's specific aim is to raise the students' achievement levels to the point where, if sustained, they would be able to pass a new state-mandated minimum-achievement test by the eighth grade. Students must pass the test, which is to become mandatory in 1990, by ninth grade in order to advance to the 10th grade.

His program, to include individual tutoring, tailored instruction and other support services such as psychological counseling, also aims to enable these students to read and do math on the ninth-grade level by the time they graduate, a standard tougher than that set out by the state's test.

"It is not an astronomically large target that we are shooting at," Masem told the board, "but it's a realistic one to move a critical mass of students to this level that will open up some doors for them."

Masem said he will bring back a detailed plan of action at the board's Nov. 4 meeting. Last night, the board gave its informal approval to continue with the plan. "Push on," said School Board Chairman Timothy Elliott.

Teachers and counselors would be required to keep detailed records of a student's progress and identify areas of weaknesses.

A part of the program would also attack identifiable hindrances to achievement, such as the lack of parental involvement and teacher and student attitudes.

About 63 percent of the city's public school students are minority students, many from disadvantaged or non-English-speaking immigrant homes.

Two years ago, the city's black elementary students scored an average of 36 percentile points lower than their white counterparts on standardized tests measuring math, reading and language skills.

Shocked by the discrepancy, Superintendent Robert W. Peebles, who retired this summer, launched a major effort to improve minority achievement. This year the system earmarked $1.2 million of its $64 million budget for programs serving underachievers.

Currently there is no systemwide standardized method, however, for improving minority achievement. It is largely left to the initiative of individual school administrators.