Montgomery County School Board member Marian Greenblatt requested yesterday that an alternative plan be drawn up for the Montgomery Blair High School area that could dramatically alter school assignment patterns throughout the lower county area in an effort to achieve racial balance.

Greenblatt's request was approved unanimously by the board during a wide-ranging discussion of possible ways to improve the ratio of white and minority students at Blair and two other high schools in the Silver Spring/Kensington area. Greenblatt's option would reduce minority enrollment at Blair, which has the highest percentage of minority students of any county high school, by erasing all school boundaries in the Silver Spring/Kensington area and dividing the area's students between Blair and Einstein High School.

Greenblatt's plan assumes that Northwood High School would be closed as scheduled next year.

The request was a radical departure for Greenblatt, who last year opposed assigning students from three predominantly white elementary schools to junior highs that feed into Blair. That assignment, supported by a majority of board members, was later overturned by the state board of education. Yesterday's discussion was part of the local board's efforts at meeting the state board's mandate to present a new plan for the area by March.

Montgomery Blair has a minority enrollment of 60 percent; the countywide average is 25.4 percent.

Superintendent Ed Andrews already has recommended one plan for Blair that would decrease the minority balance to about 50 percent by 1988. Andrews' plan includes creating an accelerated math and science program at the school and assigning students from some predominantly white elementary schools to Blair feeder schools.

After yesterday's debate, Greenblatt called the superintendent's efforts "piecemeal solving" and said that under her request the board would have to look at the area as if the slate had been wiped clean. Under her request, all students from Blair, Einstein in Kensington and Northwood in Silver Spring--including all elementary and junior high school students--would be grouped together and reassigned until minority enrollment at Blair and Einstein was in the "40 percent range." Einstein has a minority enrollment of 26 percent; Northwood has 32 percent.