After working without a contract for nearly a year, Prince George's County police officers threatened yesterday to strike or stage a work slowdown starting Saturday.

With major contract issues still unresolved, talk of a wildcat strike was fueled yesterday by anger over the recent firing of an officer for shooting an escaping shoplifting suspect, and the shooting deaths of two police officers on Monday.

Police representatives and county officials began round-the-clock bargaining at 2 p.m. yesterday in an effort to reach an agreement. Saturday is the anniversary of the expiration of the contract with the Fraternal Order of Police, the officers' collective bargaining organization.

"We're working for a settlement and we expect one," said Col. Vincent duCellier, aide to Police Chief John W. Rhoads. "This is an extremely emotional time for all of us. You can't expect the men to be happy when the administration is forced to dismiss an officer and then two officers are shot and killed. That has to have an impact on morale."

Disagreement over retirement benefits remains the major issue to be resolved in the contract talks, police officers said yesterday. The officers seek to be able to retire on a full pension after 20 years, instead of the current requirement of 25 years. Full pension benefits amount to 50 percent of a police officer's final salary.

Many officers talked yesterday of their intention to strike if there was no settlement by this morning, but other policemen said it appeared more likely that the police organization would advocate some kind of slowdown or other job action before calling a wildcat strike.

Fraternal Order of Police National regulations forbid strikes, and if the Prince George's organization struck it would automatically lose its national charter. However, it could reapply and be reinstated, officers said.

Anger in the department has mounted in recent days. Last Wednesday Rhodes fired Officer Peter F. Morgan for unsatisfactory performance. Morgan shot and killed an unarmed suspect last Christmas Eve as the the suspect attempted to flee from the Seat Pleasant police station.

A police trail board had recommended to Rhoads that Morgan be fired, but Rhoads' action led to charges that the chief "won't stand behind his troops."

Then on Monday, Officers Albert Claggett attempted to fingerprint a youth who had been seen in a car similar to one used in a Riverdale larceny.

"Even before the deaths of Officers Claggett and Swart there was a morale problem in the department, said lawyer Benjamin R. Wolman, who has often represented the police organization in court.

"The problem is the uncertainty in the area of discipline," Wolman said. "The men don't feel that they've been given a clear idea of what they can and cannot do. The guidelines simply aren't clear enough.

"You add to that what happened Monday. A lot of men are going to be upset again about the facilities in Hyattsville's holding area (where suspects are processed) and in other places in the county," he said.

"The contract is the foundation of all this," one officer said yesterday. "Morgan built it up and the shootings could be the catalyst. The guys are really ready to go."

Sources said that a member of officers in the Hyattsville station had proposed a wildcat strike Monday after the shootings only to be talked out of it by Fraternal Order of Police President Laney Hester. Hester argued that the two dead officers deserved to be buried by their fellow officers noting together, not by a group of striking individuals.

County police officers staged a job action in October 1975 to show their dissatisfaction with the county's negotiating position at that time.

During the job action police officers turned in their patrol cars en masse for repairs, many of which were trival.State police and members of the county sheriff's department worked in their place for six days until the county obtained an injunction ordering the officers back to work immediately.

The officers obeyed the injunction but the incident created a rift between the police and County Executive Winfield M. Kelly's administration that has never been repaired.

Many officers said yesterday they believed that Kelly was behind what they perceive as the county's hard line stand on retirement benefits. Many of the County's policeman have said they will work to help Republican Lawrence J. Hogan unseat Kelly in the November elections.

"We have no desire to strike, no desire to cause problems," Heater said. "But we will not let the one year go by without noting it someway."