Registered nurses who work at three Prince George's County medical facilities rejected a contract offer yesterday and voted to go on strike at 7 a.m. Monday.

Carolyn Larkin, president of the local chapter of the Maryland Nurses Association, said late last night that 86 percent of 405 nurses casting ballots voted to reject the offer from the corporation that runs Prince George's General Hospital, Greater Laurel-Beltsville Hospital and Bowie Health Center.

"I'm very concerned and very disappointed that it comes to this, but we have very strong feelings about what we deserve . . . in the way of pay," Larkin said. "What we're asking for is really professional pay for professional work."

Ken Duncan, vice president of the corporation, Community Hospital and Health Care System Inc., said the medical facilities are "ready to implement alternative staffing plans." Duncan did not give details.

The contract between the corporation, which recently took over managing the facilities, and the hospitals' 650 registered nurses has been in dispute for eight months.

The nurses had initially asked for an 11.5 percent increase in their salaries, which according to Larkin are in the $17,300 to $23,300 range and are generally less than those of other nurses in the area. In bargaining that broke off late Friday, union and corporation negotiators agreed on a 35-cent hourly pay increase retroactive to Aug. 14 that corporation officials said would give about a 3.8 percent increase.

The corporation also offered a second 35-cent increase effective next July. Union negotiators said they wanted an increase in February along with a provision to convert unused benefits into pay, or an increase to be decided through a form of arbitration. Another dispute concerned the corporation's unwillingness to grant the union request for a citizen task force to rule on union grievances about working conditions.

Also unresolved when bargaining halted were the union's request that all nurses be required to pay either dues or a fee to the union and how much pay union officers would receive while on union business.