The Montgomery County School Board decided last night to give the 13,000 county school employees their negotiated 6 per cent raises and cut back spending plans in several other areas to provide the funds.

The board's action will decrease the county's school busing program, provide for closing some schools and eliminate some teaching assistants.

It also could set up a confrontation between County Executive James P. Gleason and the 7,000 county government employees who are slated to receive only 4.2 per cent raises - the same raises the teachers and other school employees were to have received before the school board acted last night.

Despite a negotiated contract that calls for the school system to give its employees 6 per cent raises in the fiscal year that starts July 1, the County Council, which provides the money to operate the schools, cut the budget last week. The $255 million the Council approved for the schools would have provided only 4.2 per cent raises for school employees - the same as for the county workers - unless the school board cut some of its programs.

In recommending cuts last night, School Supt. Charles M. Bernardo declared: "Although we have serious concern about the cutbacks in programs and services necessitated . . . in addition to reductions already made by the (school board and council), I strongly believe that the best interests of both students and school employees will be served best by fulfilling all of the requirements of the negotiated contract."

The cuts the board approved will:

Eliminate bus transportation to school for about 6,500 students. This will be accomplished by increasing the "walking distance" - the distance outside which busing is provided - from 1 1/2 miles to 1 3/4 miles from junior and senior high schools.

Close three elementary schools in June beyond those previously approved for closing. Hillandale Elementary will be closed in June a yar earlier than originally planned. In addition, Park Street and either McKenney Hills or Oakland Terrace will be closed.

Eliminate 50 teacher assistant positions. It was not immediately clear whether these would be accomplished through layoffs or attrition.

Reduce pay for substitutes from $34 to $30 a day.

Earlier in the budgeting process this spring, cuts in the school budget resulted in elimination of such things as interscholastic sports in junior high schools and 105 summer teaching positions.