Lunches in Prince George's County public schools increased 5 cents yesterday after the county rejected a Board of Education request for $100,000 to make up for the loss of federal school lunch subsidies.

Elementary school lunches now cost 70 cents, secondary school lunches 75 cents and adult meals $1.30.

"This doesn't shock us at all," said Brian Porter of the schools' information office. "We've already seen a reduction of federal funding for free and reduced (cost) lunches and we anticipate a severe loss next year. This (increase) only bodes of things to come."

The Montgomery County school board raised prices by 5 cents Feb. 1, bringing the price of lunch at elementary schools to 65 cents and at secondary schools to 70 cents.

The cost of reduced-price lunches for children of low-income families in both counties has been raised from 10 to 20 cents.

In addition, the Department of Agriculture changed eligibility guidelines for reduced-price and free lunches, and fewer students now qualify. In Montgomery County, 1,000 students were taken off these programs starting last week. The number of families affected in Prince George's County has not been computed yet.

The new guidelines favor families of up to five members by allowing slightly higher incomes to qualify. For example, under the old guidelines, children from a family of four could get free lunches if the family's annual income was $10,250 or less. The new guidelines allow a maximum income of $10,270.

Starting with a family of six, however, eligibility income levels have been reduced.

Another change is that medical and other expenses can no longer be deducted in computing income for eligibility in a school lunch program.

"The hardship factors allowed Montgomery County to take advantage of the lunch program, because the living costs are higher here." said Joanne Styer, whose office has been swamped with phone calls from parents who received notices that their children were being dropped from the program.

Further cuts in federal school-lunch subsidies have been proposed by the Reagan administration. If they are approved, the school systems will feel the effects starting this fall.

The anticipated loss of revenue for the 1981-82 school year, estimated at around $5.1 million for Prince George's County and $2.6 million for Montgomery, would have to be made up by the county governments and through higher lunch prices, according to food coordinators for the two counties.

"When I went to the board in January, asking for the 5-cent cost increase, they told me that if the program couldn't manage on that (increase) to come back. I hope I don't have to," said Styer.

She testified before the House of Representatives' Education and Labor Subcommittee earlier this month and told its members that if the federal government goes ahead with proposed cuts, school lunches would have to be raised to $1.30 and $1.40 in elementary and secondary schools.

"If the cuts take place, next year we will have a really, really drastic problem," said Elliott B. Robertson, assistant school superintendent in Prince George's County. "Full-price lunches are currently subsidized by over 40 cents in cash and commodities. That would mean if those subsidies were lost, the person paying for lunch stands to pay 40 cents more unless the local taxpayer comes up with a subsidy."