Parris Glendening, who will take over as Prince George's County executive Dec. 6, yesterday named the five key aides who will help him run county government during the next four years.

The top appointment of the five was John P. Davey, a policy specialist at the U.S. Environmental Protection Agency, who will be the county's deputy chief administrative officer. That appointment and four others to Glendening's full-time senior advisory staff are exempt from the county's merit hiring regulations. All other appointments, including heads of departments and the chief administrative officer, are subject to approval by the nine-member County Council. Glendening has said that no action will be taken on major additional appointments until task forces he named to study county government have submitted their reports Dec. 3.

A University Park neighbor of Glendening's, Davey worked for the county personnel office from 1976 until 1980 when he went to EPA. One of his jobs will be to determine budget priorities. Davey will report to the current chief administrative officer, Kenneth Duncan, an 11-year veteran of county government.

At a brief press conference yesterday, Glendening, a Democrat who won the county executive's job in a landslide election two weeks ago, also announced he has appointed Prince George's County police officer Michael J. Knapp of Largo to act as his contact with both the county's public safety departments and the public employe unions.

Knapp, who said he plans to resign from the police department on Dec. 6, has been a negotiator for the Fraternal Order of Police -- the police union -- since 1978.

"Everyone realizes our budget constraints are a big problem," Knapp said when asked if he anticipated tough bargaining sessions with county employes in the upcoming year. Knapp said his goal was to see to it that "no one group has to bear the entire problem."

Other appointments were: Mary H. Godfrey of Mitchellville, now the county chief for employe recruitment and examination, to oversee county relations with the Washington Council of Governments, the Washington Metropolitan Area Transit Authority, the county hospital commission and the health department; Susan A. Robbins, who chaired Glendening's campaign issues committee, to review appointments to all county boards and commissions; and Fern Piret, Glendening's longtime legislative aide, to be liaison between the county executive's offive and the newly elected County Council.

Salaries for the five new senior staff members are still under negotiation, Glendening aides said. Glendening, urging citizen participation in his administration, also said yesterday that lists of jobs available in the county government and on boards and commissions are available in the county's public libraries.