Prince George's County Executive Parris Glendening said yesterday that the $526.9 million budget he releases next week will call for layoffs of approximately 400 employes in departments throughout the county government, with many of the reductions in areas untouched by cutbacks in recent years.

"There will be actual firings," Glendening said, "I guess for the first time in the history of the county, in the police department, firefighters, teachers and classified employes. There will be around 400."

Glendening said that many of those layoffs could be averted if the Maryland General Assembly passes several proposed revenue-raising measures for Prince George's. But legislative relief, if it comes, will not be available before his March 31 deadline for submitting his budget to the County Council.

Glendening added that despite his personal goal of bringing more minorities and women into county government jobs, procedures for handling the layoffs inevitably will have an adverse impact on those groups.

"We have some flexibility, but for the most part, the guiding standard will be last hired, first fired," he said.

Glendening said that his proposed budget, which the County Council must ratify by June 1, will include a list of items to be restored in order of priority if additional revenue is found.

Highest on that list, he said, will be employes in education and public safety who have been laid off, as well as heavy equipment that is badly needed by public works and public safety departments.

Representatives of the county's major labor organizations, informed of Glendening's comments, said they disagreed with the county executive's plans to spread potential layoffs throughout the government. Several hinted at the possibility of conflict that could occur later between the county's labor forces if the policy takes effect.

"Last year we took all of the damage, and in all fairness we should be exempted from any further damage," said John Sisson, president of the county's larger teachers' union, referring to last year's layoff of 507 teachers. "I think those layoffs should be suffered by other departments. Once they lay off 10 percent of the police, 10 percent of the firemen, and 10 percent of all those other departments, then it will be fair to talk about across the board layoffs."

Fraternal Order of Police vice president Thomas Lennon countered, "It would be a violation of the rights of people to lay off police officers. We don't have enough men now.

"When you talk about police officers, their citizens safety is jeopardized," Lennon said. "When you talk about teachers, you're talking about football coaches and baseball coaches and people who teach kids how to drive."

Glendening said that he needs at least $15 million in new tax revenue to avert most of the projected layoffs. Glendening said he remains optimistic that at least one of the bills, a personal property tax on business equipment that would generate $10.8 million, will win approval. He said he will continue to push for an increase in the county's surcharge on the state income tax, which would bring in $22.8 million, although skeptics in Annapolis say that measure will die.

A third bill approved last week by a House finance committee would establish a new lottery game that would raise an estimated $13 million for the county. But Glendening, noting that he expects Gov. Harry Hughes to veto that bill, said, "Lotto is a gamble upon which I would not bet."

The county government employs about 3,700 persons and another 10,670 work for county schools. While Glendening's March 31 budget will contain a dollar figure for the school system, as well as for the county, the board of education has final say about how any cutbacks should be made in its department.

The county executive's comments came yesterday during a wide ranging two-hour discussions with Washington Post editors and reporters. Glendening answered questions about such widely publicized problems as security and sexual assaults in the county jail, the recent resignation of Corrections Director Arnett W. Gaston, his own transition from two-term County Council member to county executive, and his deliberations over whether to replace the current police chief.

For the most part discussion centered on the county budget and the continual financial difficulties of coping with one of the strictest property tax limits in the nation. That limit, called TRIM, caps the county's property tax income at $144 million, the level in 1979 when the measure was approved by county voters. A move to ease that restriction failed at the polls last fall.

Although Glendening yesterday repeated his announced intention of distributing the employment cuts throughout the government, he acknowledged yesterday that "the largest cluster will come from education" because that department takes the largest share of the county's budget, about 60 percent. "But we're trying also to accommodate the fact that for the last several years they have absorbed almost all of the cutbacks," he said.