The Prince George's County school board yesterday withdrew its latest contract offer to almost 6,000 county teachers, extending a six-week-old stalemate over the teachers' demand for binding arbitration of grievances.

"The board cannot help but conclude that the teachers union is not now bargaining in good faith and may not have been, in the past," board president Susan Bieniasz said in a press conference yesterday.

The offer that Bieniasz withdrew after consulting with other board members had been rejected Monday by leaders of the county teachers' union. The offer essentially would implement recommendations of an independent labor arbitrator calling for no cost-of-living increase for teachers. The board also had offered to reduce the teachers' work year from 189 to 187 days.

The board had rejected the arbitrator's recommendation that teachers be given the right to binding arbitration in contract disputes. The board only promised to include that item in negotiations for a contract next year. The latest teacher contract expired Aug. 31.

Union leaders, responding to charges by school officials that binding arbitration was only a "leadership issue," put the board offer to a vote among its members on Monday. Union president Paul Pinsky said the board withdrew the offer before the rank-and-file tally was completed because board members knew teachers were rejecting it. He called the board action "ludicrous."

School spokesman Brian J. Porter said the board withdrew the offer because it was frustrated with union tactics in the press and with its members.

Some school board members said they opposed binding arbitration because it could tie their hands in what should be educational decisions.

Earlier this summer, they pointed out, an arbitrator ruled that layoffs affecting 150 librarians, physical education and reading teachers were done improperly following June 1982 budget cuts. The arbitrator said the teachers should be rehired and awarded $3 million in back pay. School Superintendent Edward J. Feeney dismissed the arbitrator's findings.

Yesterday, Circuit Court Judge Albert T. Blackwell ruled in favor of the superintendent in dismissing a suit by the union. Blackwell said the union should have appealed Feeney's action to the school board. Otherwise, the union was attempting to "short-circuit" the administrative process called for by Maryland law.

County Executive Parris Glendening, unaware of the board's recent action, yesterday reaffirmed his endorsement of the arbitrator's recommended settlement. "If there is not a settlement by Monday I'm going to be very irritated," Glendening said.