The budget office of Prince George's County Public Schools expects a $4 million deficit in fiscal 1980 because of increased fuel costs and the loss of some federal aid.

In its quarterly report to the Board of Education last week, the budget office predicted that even if winter temperatures are normal for the area this year, the schools will still have to pay $2.2 million more for heating than allotted in the fiscal 1980 budget.

Budget planners noted in the report that the cost of fuel oil has risen in the past year from 43 to 67 cents a gallon, a 55 percent increase. In addition, the average cost per kilowatt-hour of electricity has gone up from 5.2 to 6 cents.

These increases, plus the loss of $1.7 million in federal impact aid, have raised the specter of a $4 million deficit next June, according to budget officals. Federal impact aid is money given to the local government to compensate for lost tax revenue from parents of public school children living on federal property.

"This won't have any concrete meaning until we find out what kind of winter we'll have," said Eliott Robertson, assistant superintendent for budget, management and finances. "All we're telling the board is we have a potential problem and they may have a potential problem and they may have to ask for a supplemental appropriation from the county."

Robertson said the budget office has recommended that the schools not ask the county for supplemental funds yet, but wait until the first half of the fiscal year is over.

According to Robertson, the county schools have rarely had to worry about budget deficits. "I remember once coming out with only $99,000 over our appropriation, but never coming up with a budget deficit," he said.

He said the only time that he could recall having to ask the county government for supplemental funds was when the desegregation order requiring massive busing was issued. The request was turned down.

Robertson did note, however, that the schools sometimes have to ask for county money to cover expenses, until state grants arrive later in the year.

School budget analysts also predicted that the system may face a $135,000 deficit in the pupil transportation budget because of an increase in the cost of replacement buses.

"We're usually able to adjust to small fluctuations in our budget, but the size of this shortfall will almost surely force us to go back to the county for a supplemental appropriation in the winter," said Robertson.