Convicted felons hired by the city government as part of a parolee work program ordered by Mayor Marion Barry were employed at the city police department, and police officials are concerned that investigations and identities of undercover officers and informants may have been compromised, police sources said yesterday.

At least three inmates in the program were working at the police department's 4th District station during the planning of Operation Caribbean Cruise, the sources said. The operation, the largest ever in the city with 69 houses raided in a search for drugs and weapons, failed because word of the raids apparently leaked out to the suspects.

Police officials, sources said, are also concerned that undercover and plainclothes officers and police informants may have "blown their covers" if paroled inmates employed by the city spotted them in a police facility.

The inmates were placed in the police department as part of Barry's Special Temporary Employment Program, a work program under which paroled inmates are hired by the city and placed in government agencies by the D.C. Office of Employment Services.

The program, begun last March, was designed to help relieve overcrowding at the D.C. Jail by creating jobs for inmates who would not be eligible for parole without employment.

Besides the 4th District, the inmates worked at the 5th District, 1st District substation and police department headquarters, officials said.

The inmates worked primarily on cleanup crews and apparently had keys to offices and widespread access to most areas of the buildings, including sensitive work places and employe locker rooms.

Sources said that police officials apparently did not know that the department was involved in the program. They learned of the department's participation when officers investigating crimes noticed that they were locking up persons they had seen working in police facilities.

In one case, sources said, police arrested a man for stealing a bicycle from a police locker room and discovered that the man and his supervisor were paroled inmates placed at the police department as part of the work program.

Lt. William White III said that Police Chief Maurice T. Turner Jr. ended police participation in the program yesterday because of concern over security issues.

Sources also said that police are investigating the possibility that one or all of the three inmates at the 4th District station, who started working there Jan. 21, may have compromised the secrecy of Operation Caribbean Cruise.

Part of that investigation is also focusing on the theft, shortly before the operation, of a police department radio from the 4th District radio room.

The city's Department of Administrative Services placed 15 inmates in positions in the police department before police canceled the program, according to Linda Boyd, a spokeswoman for Administrative Services. Boyd said that apparently no one in the police department was told that the workers being detailed to the department were part of the inmate work program.

"This is a prime example of political considerations outweighing the needs of effective law enforcement," said Gary Hankins, labor committee chairman of the Fraternal Order of Police.

"They furloughed inmates are all over the department. I don't think we need to look much further than this to see that Operation Caribbean Cruise or any other police operation under way while the STEP program was in effect should be considered compromised," Hankins said. "There should be a complete review to protect the officers, informants and the investigations."

According to Jacqueline Threadgill, a spokeswoman for the D.C. Department of Employment Services, the three inmates working at the 4th District station during the planning for Operation Caribbean Cruise were placed at the police department by the city's Department of Administrative Services as part of STEP.

The three have been arrested a total of 18 times since 1975, according to police department records, and all are on parole.

They have a total of seven felony convictions on charges that include armed robbery, possession of heroin, grand larceny and first-degree theft, the documents show.

In addition, one of the inmates tested positive for PCP in a drug screening test administered in June 1985 while he was on parole, according to police records.

About 530 police officers were involved in the Feb. 22 operation, designed to break the back of a Rastafarian drug network operating in Northwest and Northeast Washington by simultaneously executing 69 search warrants.

Though police expected to seize huge caches of illegal drugs and automatic weapons and arrest as many as 200 people in the raids, only 27 were arrested and police seized about $20,000 in drugs and 13 weapons, none of which were automatic.

STEP was begun in March 1985 "to provide work experience for recently paroled offenders who need a job opportunity in order to be released," according to Carolyn Jones, director of the Department of Employment Services office of job services.

She said 259 inmates, most convicted felons, have taken part in the program, which according to city administrator Thomas Downs was undertaken so the District government could set an example and persuade local private businesses to hire parolees.