Montgomery County School Superintendent Wilmer S. Cody yesterday outlined a major plan to try to improve the academic performance of black and Hispanic students in the county schools.

Cody, formerly superintendent of the Birmingham, Ala. schools when minorities made significant gains in achievement there, told a packed school board meeting that he will appoint a group of staff members to decide how to narrow the historically wide gap between whites and Asians, and blacks and Hispanics, on standardized school tests.

Cody's announcement of the plan was, in part, a response to demands from the minority community recently made on the school system, which is recognized for its ability to educate white and relatively affluent students. Those demands peaked earlier this summer when school officials announced that two out of three black ninth graders in the county and one out of two Hispanic students failed a state math competency exam, a showing far worse than white or Asian students.

The school board voted earlier yesterday to make improvement of minority performance one of its top goals over the coming years. Minorities make up 25.4 percent of the school system's 92,517 students.

Cody's team is expected to come up with a plan for evaluating all schools and subject areas for failure or success in instructing blacks and Hispanics. It is also charged with reviewing the disproportionately low representation of these students in advanced courses, devising an extensive plan to involve minority parents in education, and conducting a national search for programs that have succeeded in bringing about substantial gains in minority achievement.

"I am encouraged," said James Robinson, chairman of an independent citizens' group representing civic and black organizations. "It is the first positive sign I have seen out of a combination of school administration and board members in many, many years. It is the first time they have acknowledged there is a problem . . . and they are willing to do something about it . . . . "

Cody's plan highlights questions facing a number of suburban school systems around the nation as minority populations continue to expand into their areas.The plan, which was endorsed by the board, also marks one of the most important and significant acts taken by the board in its almost yearlong effort to end the discord that existed between the county's minority community and the school system during the last four years.

The board majority during that period was swept out of power in November by four new board members who, with the support of a broad coalition of civil rights and minority activists, charged that the former board had taken a number of steps that were insensitive to minority concerns.