The Montgomery County Council yesterday approved a $662 million budget for next year that will cost the owner of an average county home an additional $50 in property taxes.

The 1981 fiscal year budget, up 8.3 percent from this year, provides substantial funding increases for transportation and housing, and only a modest increase for education, which school administrators say may result in some teacher layoffs.

Although the council cut $2.8 million from county executive Charles W. Gilchrist's proposed budget, it followed the general priorities he had set.

Council president Scott Fosler said he was pleased that the 8.3 percent increase in the budget is lower than the inflation rate. "The careful work of all the past three months has enabled us to reduce costs, while avoiding cuts in vital services and allowing for program improvements where they are needed," Fosler said.

However, Wylie Barrow, chairman of the Montgomery County Taxpayers League, criticized the council for raising property taxes despite having a $35 million surplus from the current fiscal year. Most of the surplus -- about $28 million -- will be used during the 1981 fiscal year.

"They always say the surplus is going to be a lot less than it is," said Barrow. "They should use that money to reduce taxes, and instead they just keep spending."

Council member Neal Potter said the surplus resulted mostly from the rise in real estate values, which has brought the county more money in property taxes than it expected.

Property in the county is assessed at 45 percent of market value. The proposed budget will raise the county tax rate from $3.08 to $3.20 per $100 of assessed valuation.

The new property tax rate will not apply equally to homeowners, since one-third of the homes in the county are being reassessed this year. The $50 tax increase would apply to a homeowner whose house is now assessed as $40,000 and has not yet been reassessed. The owner of an identical home that has been reassessed will have a tax increase of about $200.

The council cut 326 of the school system's 5,401 full time teaching positions -- 64 more positions than the board of education had elected to cut.

The board felt it could eliminate some teaching positions because of declining enrollment, but school spokesman Ken Muir said there's now a possibility there will be teacher layoffs for the first time.

"It'll depend on how many teachers go on leave, and on the number of retirements and resignations," said Muir.

Council member Neal Potter said the council's cuts and teacher positions would not affect the ratio of teachers to students. Muir agreed that the overall ratio would remain the same, but said that some class sizes might not be "as good" as this year's.

About 50 of the teaching positions were cut by following the recommendation of Supt. Edward Andrews and abolishing the seventh period of the day in the county's senior high schools. For most students it's a free period, but some will end up taking one less course. The extra time will be redistributed among the six remaining periods.

Gilchrist had proposed cutting 52 administration positions from the school system's five area offices, but the council cut only eight of those positions. Gilchrist said he had "reservations" about that decision, but he otherwise felt that the council had acted "very responsibly" in its decisions on the budget.

The mass transit system budget was increased the greatest percentage of any item, to $30.7 million, up 25 percent over last year's budget.

The increase will be used a finance the operation of 33 new buses and about 50 new employes, most of them bus drivers.

The funding for county government operations, the second largest item in the budget at $166 million, would increase six percent, the lowest percentage of any item compared to last year's budget.