The Montgomery County Council voted yesterday to spend $7.5 million in county funds to build a junior high school in Germantown to relieve overcrowding in several upcounty schools.

The state, which usually funds school construction projects, gave the county money to plan the school two years ago, but rejected the county's request for construction money last year.

Council members hope that if the Germantown school is made the county's top priority project this year, the state will reimburse most of its cost.

"I think we're taking a calculated risk if we fund it ourselves, but I don't think we have any choice at this point," council member Michael Gudis said.

For months school officials, school board members and Germantown parents have urged the council to build the school to relieve overcrowding at Montgomery Village, Ridgeview and Gaithersburg junior highs.

Enrollment at these schools last year was 3,337, 10 percent above planned capacity of 3,045.

The new school, to be called Martin Luther King Junior High, is expected to open in September 1971 at the intersection of Rte. 355 and Neelsville Road and serve 1,050 seventh through ninth graders.

The council's vote was 6 to 0, with Council President Neal Potter abstaining. He called projections of student enrollment and cost estimates inadequate and said he wanted the county to have a stronger case to take to state officials.

Potter said busing students to less crowded schools further south in the county might be cheaper than building a new school.

The county plans to finance construction through sale of bonds. Potter said the annual debt service the county would have to pay on these bonds -- about $700,000 -- plus an approximately equal sum required to run the school might necessitate adding two cents to the county's real estate tax rate or eliminating 65 teaching jobs.

Council member Scott Fosler said building a new school would be better for the community than alternatives such as busing or redrawing attendance districts of existing schools.

"In the past, we've built schools where children are and I don't see any reason for changing that policy," Fosler said.

County Executive Charles W. Gilchrist repeated his support for building the school with local funds, but urged a commitment by the Board of Education to make reimbursement its first priority in its request to the state.

Many county officials are convinced that future population growth in Montgomery will follow the I-270 corridor to Germantown where housing prices are lower than in densely developed lower-county communities where enrollment is declining.

"I can't prove it," Gudies say, "but I have a gut feeling that growth in that area is going to be larger than what we're seeing now."