The FBI is investigating allegations of corruption in the enforcement of drug laws by the D.C. police department, sources said yesterday, adding another agency to the list of city departments under federal investigation.

The FBI is said to be investigating an alleged pattern of police officers personally profiting from their handling of drug trafficking cases. Allegations also have been made to federal authorities that internal departmental investigations of such misconduct have been covered up, sources said.

A source who is knowledgeable about the investigation said that FBI agents have interviewed several D.C. police officers who have said that other officers have kept drugs and money taken in drug raids, falsifying official reports by listing only a portion of what was taken. FBI agents also have questioned some convicted drug dealers about the amounts of drugs and money seized by officers, according to the source.

Police Chief Maurice T. Turner Jr. said he was unaware of any such activity by officers and denied that any police officials or officers have engaged in improper conduct. "I haven't heard of any federal investigation. I have no knowledge of it," Turner said. "If the federal investigators have something then they should come forth with it."

The investigation of alleged police corruption is a major new element in a broad array of probes that includes inquiries into the awarding of numerous city contracts, possible obstruction of justice by associates of Mayor Marion Barry and expenditures made from the mayor's office accounts.

Enforcement of drug laws and drug use by city employes and officials have surfaced repeatedly as key elements in several aspects of these investigations.

Karen K. Johnson, a convicted cocaine dealer, has told prosecutors that she sold cocaine to Barry on 20 to 30 occasions and sometimes was paid for the drugs by check, sources said. Barry has denied buying or using drugs.

In addition, FBI agents during a May 22 search seized small quantities of white and green powders, which sources have said were identified as cocaine and marijuana, from the town house of top Barry aide David E. Rivers. Rivers, who is on leave from his post as secretary of the District of Columbia, has not been charged.

An attorney for Rivers has said his client has done nothing improper.

Barry has made drug enforcement a centerpiece of his administration, backing tougher penalties for drug dealers and pumping millions of dollars into Operation Clean Sweep, a massive police program aimed at clearing the city's neighborhoods of drugs and drug dealers.

Disclosure that members of the police department are under investigation comes one day after Barry denounced the ongoing federal probe as a "Mickey Mouse kind of operation" and called on members of the news media to be "heroes" and stop reporting on prosecutors' activities.

Some sources, meanwhile, have described the investigations as extraordinarily ambitious undertakings that touch all major city agencies, and potentially a wide range of the top officials in the Barry administration.

Search warrants executed on May 22, the day federal law enforcement officials concluded a 17-month undercover phase of the contracting probe, cited the federal Racketeering Influenced and Corrupt Organizations Act.

The law, crafted to attack organized crime, allows prosecutors greater flexibility in presenting evidence to show the existence of an enterprise marked by a broad pattern of corruption.

In an interview yesterday, Barry said he was not aware of a federal investigation of alleged police corruption and denied that there are improprieties in the 3,880-member department.

"This is dangerous business here. These are serious allegations. This has gone from the sublime to the ridiculous," Barry said.

A spokesman for U.S. Attorney Joseph E. diGenova declined comment yesterday on reports of a police corruption probe.

An FBI spokesman also declined to comment last night.

Gary Hankins, bargaining agent of the Fraternal Order of Police, said of the allegations of misconduct, "If it's true, it's a shame. Anybody who's guilty of that kind of activity, no matter what their rank, should be held accountable."

The probe of alleged police corruption is the first in the District since the 1950s. In recent years, the D.C. police department has been regarded as a highly respected law enforcement agency, mostly free of the corruption that has plagued other large police departments such as New York, Philadelphia, Miami and Houston.

The department's drug enforcement programs have resulted in a threefold increase in drug arrests over the past seven years. More than 12,700 persons have been arrested on drug-related charges under Operation Clean Sweep, which began a year ago this week.

Operation Clean Sweep is considered one of the nation's most innovative drug offenses, using such tactics as roadblocks, car seizures and the controversial "reverse buy busts," in which officers posing as drug dealers sell to unsuspecting buyers.

At a news conference last week marking the operation's first anniversary, officials said that more than $10 million worth of PCP, cocaine, marijuana and heroin has been seized during the operation, along with $950,000 in cash, 351 vehicles and 632 weapons, mostly handguns.

Accusations involving drugs and drug use have hung over the Barry administration since its early years, when federal prosecutors investigated allegations that the mayor had used cocaine in a downtown nightclub.

Allegations of drug use involving city employes, including Barry, surfaced again in 1983 and a federal grand jury heard testimony that led to the conviction of Karen K. Johnson, with whom Barry has said he had a "personal relationship."

Johnson, who was sentenced to four months, was also jailed for eight months after she refused to testify to the grand jury investiga- FBI "should come forth" with allegations.

-- Chief Maurice T. Turner Jr.

ting drug use by city employes.

Johnson is cooperating with federal authorities and has told prosecutors that she received $20,000 to $25,000 in hush money from two city contractors in return for refusing to testify.

John B. Clyburn, a D.C. businessman who is a close friend of Barry's, has acknowledged making payments to Johnson, but has said the money had nothing to do with her refusal to testify, according to sources. A second prominent city contractor, Roy Littlejohn, has acknowledged providing funds for Johnson through Clyburn, but denied that it was hush money, sources said. Littlejohn, in a statement released last week, denied that he acknowledged making payments to Johnson.

In addition, a longtime associate of Barry's, Herbert Young, has been indicted on cocaine distribution charges as part of the current investigation. Young has told acquaintances that the FBI wanted to question him about $41,000 in city business he received after he notified Barry that FBI agents were outside the mayor's house in a car.

Sources have said that the FBI is trying to determine if Young was able to obtain confidential information from FBI clerks and then passed the information on to associates of Barry. Young has denied obtaining confidential information and Barry has denied receiving any. Staff writers Sharon LaFraniere, Victoria Churchville, Michael York and Tom Sherwood contributed to this report.