Prince George's County Executive Lawrence Hogan said yesterday that he has signed his own contract with a county public employes union that has threatened to walk off the job next Monday.

Union representatives said yesterday that they knew nothing of any such contract and that Hogan's office refused to tell them what it contains.

Hogan also refuses to discuss the contract he signed and his aides said its contents would remain a secret until a federal mediator examined it and called a meeting with the union to discuss it.

Hogan's press release on the subject said only that the 1,500 workers represented by the American Federation of State, County and Municipal Employees would receive a 4.7 percent pay increase this year and 5 percent next year.

Ernie Crofoot, executive director of the union, said yesterday, "This is so incredible, I thought I'd seen it all. Maybe someone will be kind enough to offer us a copy when we're in Upper Marlboro tomorrow."

Hogan and the union have been battling over a new contract for over a year. The union's members are among the lowest-paid county employes.

Last month Hogan's negotiators and the union reached a tentative agreement that provided for wage increases of 4.7 percent this year and 5 percent next year and which his own aides felt was favorable to the county.

Although the union membership ratified that agreement, Hogan refused because he apparently felt that recent conflict with political adversaries on the County Council over his handling of the labor negotiations would make a settlement appear to be a capitulation.

Several days after he rejected the agreement, Hogan said that several minor economic issues had been unacceptable to him.

Since then Hogan has said that he would not sign the agreement because it provided for a county-paid shop steward and allowed paid days off for union business.

The union has accused Hogan of bargaining in bad faith and recently filed an unfair labor practices charges against the county. A ruling on that charge is expected this week.

Last week, the union also notified the county that it would go on strike next Monday if no settlement in the contract dispute was reached, Prince George's County is the only jurisdiction in the Washington area that gives its employees the legal right to strike.

A strike by the union would deprive the county of the services of landfill crews, building inspectors, some secretaries, maintenance workers and jail guards, among others.

Since the union declared its intention, Hogan has devised a series of legal maneuvers designed to delay or challange a strike.His announcement of a new contract yesterday was described by aides as a final effort to avert a walkout strike.

Although Hogan's aides would not discuss specifics of the contract, they said the county had agreed to compromise on several outstanding issues.