Nurses who staff three medical facilities in Prince George's County, including the general hospital in Cheverly, will walk off the job at 3:30 p.m. today if a contract dispute with the corporation that runs the facilities is not resolved, an official in the nurses' union said yesterday.

According to union officials, negotiations are continuing through a federal mediator. Because the mediator has imposed a news blackout on the discussions, neither side would discuss the negotiations or whether any progress had been made.

The union represents 650 registered nurses at Prince George's General Hospital, Greater Laurel-Beltsville Hospital and the Bowie Health Center. At last report the nurses were asking for an 11.5 percent wage increase, more educational benefits and an agency shop that would require all nurses to pay a fee for union representation.

The Community Hospital and Health Care Systems Corporation, which this year took over management of the county-owned medical facilities, has offered the nurses an average 3.3 percent wage increase. The corporation has proposed eliminating automatic step-pay increases and allowing instead only discretionary merit pay raises.

The two sides have been negotiating since February and the nurses have been working without a contract since Aug. 15. Last week the union membership voted to go on strike if there were no contract agreement by today.

Talks broke off last Friday when both sides accused each other of not providing counteroffers. On Tuesday the union filed unfair labor practice complaints with the National Labor Relations Board, claiming that the hospitals had given out false information to union members about negotiations.

On Wednesday a federal mediator stepped in and imposed a news blackout on the talks that will not be lifted until this afternoon.

Ken Duncan, vice president of the new hospital corporation, said earlier this week that his staff was preparing for a possible strike. He said that if a strike occurred there would be adequate nursing staff to keep the facilities running. He declined to say how the hospitals would arrange for replacements.

Duncan also said that the health facilities are having financial difficulties and cannot afford now to pay the nurses what they are asking. Duncan has said he feared that if he gave the nurses a large pay increase, other hospital workers would demand the same.

Carolyn Larkin, president of the nurses' local, said the union members currently earn between $17,300 and $23,300 per year. Beginning salary is $8.36 per hour, which would be raised to just over $9 per hour if the nurses get the raise they have asked for.