The FBI has begun investigating whether 4th District narcotics officers took payoffs from drug dealers in exchange for information about Operation Caribbean Cruise, a much-vaunted drug sweep that resulted in an unexpectedly small number of arrests, sources said.

Federal agents on Thursday visited the 4th District police station in Northwest Washington looking for records of the drug crackdown, sources said.

Their visit was the second in three days. On Wednesday, federal agents armed with subpoenas searched for records in connection with an investigation of whether 4th District officers kept drugs and money seized in drug raids.

That investigation focuses on about five officers, including Shelton D. Roberts and his partner, James Whitaker Jr., according to sources. Attempts to reach Roberts for comment have been unsuccessful. Whitaker, though his attorney, has denied any wrongdoing.

The FBI began a narrowly focused investigation into the alleged skimming operation some months ago with the secret cooperation of some D.C. police officers. The bureau did not inform police officials of the probe until August 27, when The Washington Post disclosed the investigation in a news report.

That probe was expanded recently to include the handling of Operation Caribbean Cruise, including the actions of Roberts, sources said.

Operation Caribbean Cruise was aimed at what was described as a heavily armed network of Jamaican drug dealers. Though 550 officers and support personnel fanned out over the city in a coordinated raid on Feb. 22, 1986, only 27 drug suspects were arrested and $20,000 worth of drugs seized.

After the raid, police officers told the department's Internal Affairs Division and Police Chief Maurice T. Turner Jr. that Roberts may have tipped off drug dealers, sources said.

The U.S. Park Police, which participated in Caribbean Cruise, also turned over information to the Internal Affairs Division about a stolen 4th District police radio that was allegedly provided to a raid target.

At a news conference on April 16, 1986, Mayor Marion Barry said that an internal police investigation had pinpointed the source of the leaks leading to the failure of the drug raid. But Barry said he and Turner decided not to make the findings public because to do so might jeopardize future secret operations.

Turner, in an interview last month, said the Internal Affairs Division had been unable to prove allegations of leaks to drug dealers. "We still have some aspects of that investigaiton that are currently being conducted and it wouldn't be fair of me to comment on those," Turner said then.

Officers also told Turner and the Internal Affairs Division that some 4th District officers were skimming drugs and money from drug raids, sources said.

When it appeared to the officers that the police chief and the internal affairs unit took no action on the allegations, the officers took the information to the FBI, which launched an undercover probe, sources said.

On Wednesday, police officials revoked the police powers of Roberts and Whitaker -- a disciplinary action one step short of suspension. The officers, both 17-year veterans of the police force, were given jobs in which they will not come in contact with the public, sources said.