Prince Geroge's County's dead-locked union negotiations emerged from the back rooms and into the public eye yesterday when, at a morning press conference on an unrelated subject, County Executive Lawrence Hogan got into a heated argument with a union leader who had come to the conference to confront him.

As television cameras whirred and Hogan's own aides gaped, the county executive departed from his preannounced discussion of county hospitals and harshly criticized his labor negotiators. He accused the County Council and union of trying to manipulate him, and denied any responsibility for a stalemate in contract talks that has led to the possibility of a strike sometime within the next two weeks by 1,500 county employes.

"I'm not going to be pressured into an agreement," Hogan said, gesturing across the heads of reporters at union leader Edna Barry as Hogan's aides nervously nudged each other to, as one said, "get him out of here."

As the argument evolved into a dispute over specific contract items, including personal leave days and the county's percentage of some medical costs, Barry shot back across the room: "Mr. Hogan, we're talking about pennies now. How can we settle this thing if you won't tell us what you want?"

Not surprisingly, no settlement on the longstanding contract dispute was reached at yesterday's press conference. But one point did become clear: With only a few minor issues unresolved, the conflict between the two sides is as political as economic in nature.

The five locals in the American Federation of State, County and Municipal Employees (AFSCME) have been negotiating with the county for a new contract since last February.

Since July, the county employes who operate snowplows, repair county roads, guard the county jail and provide clerical and janitorial services to every county office, have been without a new contract and without the raise given to all other county workers.

Last Wedndesday the contract dispute appeared to be resolved when Hogan's own negotiators and those of the union signed a tentative contract that by all accounts was quite favorable to the county. But in a late-hours session that night with his aides and negotiatiors, Hogan vehemently rejected the agreement, saying it would look as if he had capitulated to pressure by the County Council and the union, both of which had publicly pressed him for a resolution of the dispute.

What apparently pushed Hogan to say that he would not approve the agreement were recent statements by council members -- principally Chairman Parris Glendening, whom Hogan publicly admits he dislikes -- criticizing the county executive and his efforts in the negotiation process.

Since Hogan and the council were elected a year and a half ago they have bickered continuously over their separate powers, political philosophies, personalities and the executive's most prized prerogative, appointments.

With that backdrop, Hogan told his aides and negotiators he would approve the tentative agreements only is the union agreed to publicly criticize the County Council and, specifically, Glendening.

When county officials and union representatives met last Thursday in one more effort to solve the contract dispute, union officials refused to sign a statement criticizing the council and also refused another Hogan condition of removing the union's business manager for Prince George's, Paul Manner. Relations between Manner and Hogan have not been friendly ever since the union chief and AFSCME supported Hogan's opponent in the 1978 county executive race.

"It was pure blackmail," Manner said of the request by Hogan to criticize the council and remove him. "It was essentially saying, if you sign this you have an agreement. The only problem Hogan had with that agreement, despite what he says now, was a political problem."

Hogan denies that political considerations led to this rejection of the tentative contract and says his labor negotiators "exceeded their authority in agreeing to some economic issues that he could not approve.

Privately, several council members said they were surprised at Hogan's intractable stance. "The poor union has practically been groveling on its stomach and he keeps backing them into a corner," one council official said.

Said another, reflecting on the last week's events, "Apparently, Hogan's gone berserk."

Despite Hogan's refusal to accept the tentatively agreed-on contract, 600 members of the union met Monday night and voted unanimously to accept it. They also voted unanimously to support a strike if union leaders call for it and to support the filing of an unfair labor practice grievance against the county for failing to support the tentative agreement after it had been signed by Hogan's negotiators.

The union membership did not consider a last-minute contract proposal put forward by Hogan's office Monday afternoon because the proposal was never brought to an official negotiating session, union representatives said yesterday. The proposal submitted Monday varied only in slight degree from the tentative agreement signed last week.

Manner said the union will wait several days before deciding whether to give the county government the required 10-day notice needed to legally strike. "We feel the ball is in his court now. Obviously we feel the decent thing to do would be to approve the contract."

A press release issued by Hogan's office yesterday stated that "the county executive's office does not think the union is acting in the best interest of its members by threatening to file a frivolous, unfair labor practice charge when the county has made a very generous and responsible offer," a reference to the proposal by Hogan's office Monday that the union membership did not consider.