Prince George's County Executive Parris N. Glendening said yesterday that next year's operating budget will mark the first time since voters passed a property tax cap six years ago that the county has not been forced to impose a hiring freeze or reduce services in order to pay its way.

Glendening, who is scheduled to present his budget recommendations to the County Council March 28, did not present specific figures for the fiscal 1986 budget in the interview. But he said that $7.2 million is expected to be added to county revenues next year because of a change in the property tax limit approved by voters in November. That change will allow the county to attain a measure of "fiscal stability" that has been lacking in recent years, Glendening said.

"We've gone through a threshold and I predict that we'll be stable for at least three more budgets," he said in an interview. "We are not in a position to go through the second threshold of improving services . As a result, I think we're losing a lot of our potential."

Glendening has long been a critic of TRIM (Tax Reform Initiative by Marylanders), the county charter amendment that was passed in 1978 and limited county property tax revenues to $144 million. He campaigned for the modification passed by voters last fall that ended the cap but instead froze property tax levels at $2.40 per $100 of assessed value.

Despite the increased revenues next year, Glendening has warned that some county services, especially schools and public safety, will still be underfunded. He and other officials said the emphasis in the 1986 fiscal year will be on maintaining services rather than adding to or improving on what already exists.

Under TRIM in past years, the county has been forced to reduce personnel to meet the budget. In the current fiscal year, running from July 1 to June 30, 300 positions were eliminated from the county's $579.1 million budget. Also, $7.7 million in state education aid and another $7.3 million in new transfer tax revenues were added to county coffers to balance the budget. In 1982, 500 teachers were laid off so that the school department could make ends meet.

John Wesley White, the county's chief administrative officer, said that according to "a theoretical economic model," the county's 1986 annual budget will have to rise by 5 percent -- to about $607 million -- in order to account for inflation. But projected revenues, Glendening said, will fall about 1.5 percent -- or $5.3 million -- short of what is needed to maintain current service levels.

By contrast, Montgomery County Executive Charles W. Gilchrist has proposed an 8.7 percent increase in the county budget, which would raise it to $960 million for a county with nearly 100,000 fewer residents.

Fairfax County and Alexandria officials have proposed spending increases for next year of 5 and 10 percent respectively.

The $5.3 million funding gap will be erased, Glendening predicts, if the General Assembly approves legislation pending in Annapolis this session giving the county power to impose a new commercial utilities tax. That could raise an added $10 million in 1986, Glendening has said.

But that bill has yet to be introduced in the General Assembly and legislators said yesterday that it is unlikely it will pass.

Glendening has warned, however, that a maintenance budget will mean that certain crucial services in the county will remain underfunded. Losers will be the county's public schools, which have asked the county to provide an added $2.3 million needed to decrease class size by an average of one student per class.

Also lost will be any county effort to replace aging fire equipment and buy new mobile paramedic units.