Prince George's County Executive Parris Glendening, in an effort to control a looming $30 million budget deficit, announced yesterday that he has imposed a hiring freeze on county jobs, moved to eliminate all cost-of-living increases for county employes next year, and is cutting out funding for virtually all vacant positions from next year's budget.

Glendening termed those steps "drastic" and "unfortunate," but said they were necessary to begin meeting what county officials estimate will be $30 million in costs over a projected fiscal 1984 revenue of $526.7 million.

Despite these steps, he said, hundreds of employes will still have to be laid off if the county does not receive additional money. He declined to say how many positions would be terminated, though he has put earlier estimates at 600 or more.

Approximately 120 of the county's 3,900 positions are currently unfilled, budget officials say, with the majority of the vacancies in the police department and the departments of public works and transportation.

Most of the 49 vacancies in the 1,281-member police department were going to be used to hire uniformed officers for walking patrols, burglary prevention units and other programs fashioned in response to public outcry, according to police chief John McHale.

"This is no surprise," McHale said yesterday, reflecting a resignation that has become increasingly common among employes of this financially strapped county.

"We've been following the executive's efforts to get additional funding and we realize that if there's no additional funding, you have to cut back."

Other department heads expressed concern about the quality of the services they will be able to offer.

"If the trend continues, we're not going to be able to make some of the inroads we'd like to make," said Fire Chief Marion H. (Jim) Estepp, head of the county's 500 paid firefighters and approximately 1,000 volunteers. Estepp said his department currently has at least two vacant civilian positions, as well as four vacancies for firefighters.

County inspections of everything from restaurants to construction projects "are going to have to be more superficial and perhaps less timely," said Eugene Lauer, acting director of the department of licenses and permits that has seven vacancies for inspectors.

Prince George's fiscal problems began with the 1978 passage of the TRIM amendment that put a cap on the amount of money the county can collect from property taxes. That limitation showed up dramatically this school year, when 507 teachers were laid off.

Glendening, since his election by a landslide last fall, has lobbied with the state legislature for its approval to put several tax proposals in place. He sought to impose a one-cent local sales tax, but abandoned the plan when the governor and General Assembly leaders insisted the measure wouldn't pass.

He then began a push for increases in the personal property tax, which largely affects businesses, and in the county's surcharge on the state income tax. Though those measures passed the delegation of local legislators after intensive lobbying last week, the bills face major opposition from Assembly leaders.

Budget officials estimated yesterday that the county will save $600,000 from now until the end of the fiscal year on June 30 by imposing the hiring freeze.

Glendening, who received much of his early support in his campaign for executive from representatives of the county's labor unions, said yesterday "I think it's unfortunate that the public employes bear an undue burden for the situation before us."