The Montgomery County Council reversed an earlier decision yesterday and decided not to finance a 13-room addition at Oakview Elementary School, a move that school officials said jeopardizes their plan to desegregate several predominantly minority schools in Silver Spring.

The council's surprise action was the latest twist in an ongoing debate over how to improve racial balance in lower Silver Spring, where minority enrollments now average 60 percent.

The debate centers on the school board's plan to improve integration in 13 schools, known as the Blair cluster schools, by pairing Oakview with New Hampshire Estates. The school board had asked the council to fund the additional classrooms at Oakview to accommodate students sent there from New Hampshire Estates, where minority enrollment is 91 percent.

School board President James Cronin said the council's decision effectively kills the pairing and leaves the school board without a viable desegregation plan.

"They have substantially impaired if not destroyed the integration effort" in schools in that section of the county, he said.

School Superintendent Wilmer S. Cody agreed: "It puts the whole plan in jeopardy. We'll have to go back and review the situation."

School officials had hoped to reduce the number of minority students at New Hampshire Estates by pairing the school with Oakview's regular school program, which has a minority enrollment of 70 percent. As part of the plan, Oakview's special Spanish immersion program would have been transferred to another cluster school, Rolling Terrace Elementary, to help reduce minority enrollments there.

Oakview community leaders, who have voiced doubts about whether the plan would improve racial balance, vigorously opposed pairing their school with New Hamsphire Estates and asked council members not to fund the extra classrooms at Oakview. "We are very happy that they made that decision," said Dale Majerle, an Oakview civic leader. "In our estimation they did what was right fiscally and in every other way possible."

Yesterday, after council President William E. Hanna asked that the council reconsider its earlier decision, council members voted 4 to 3 against funding the additional classrooms at Oakview. Hanna was joined in voting against the addition by council members David Scull, Esther Gelman and Rose Crenca.

Hanna said the extra classrooms at Oakview would bring New Hampshire Estates' minority enrollment down only to 87 percent. He said Cronin's claim that the school board's desegregation plan has been impaired is "baloney."