When FBI agents secretly penetrated the D.C. police department a year ago, their action violated a protocol cherished within the fraternity of law enforcement agencies and signaled deep-seated skepticism among officers about the department's ability to police itself.

The FBI probe of alleged police corruption, preempting the watchdog role of the department's Internal Affairs Division, appeared to give credence to suspicions that Internal Affairs and top officials in the department cannot be trusted to pursue corruption cases vigorously.

Those suspicions, mounting over the years within a community of disaffected officers, union officials and outside critics, have been

fueled in the past year by allegations that the elite 50-member unit has allowed tampering with drug test results and has failed to investigate allegations that some 4th District vice officers skimmed cash and drugs from raids and tipped drug dealers to a massive 1986 drug raid dubbed Operation Caribbean Cruise.

"It has not escaped anyone's observation that in recent memory the Internal Affairs Division has never successfully investigated any high-ranking official in this department or in the District government," said Gary Hankins, labor committee chairman of the Fraternal Order of Police.

"When the perception among the rank and file is that you put on a cloak of protection when you put on a white shirt, you destroy the very underpinnings of discipline," Hankins said, drawing a distinction between the rank and file "blue shirts" and those above the rank of sergeant who wear white shirts.

Police Chief Maurice T. Turner Jr., who was not informed by the FBI of its undercover probe of the skimming allegations, has denied that Internal Affairs has covered up or failed to investigate sensitive cases. Last week, he ordered ranking officials not to answer reporters' questions about the unit, which has a $1.4 million annual budget.

Though Turner will not publicly discuss the continuing FBI investigation, a ranking police source said last week that top police officials believe that Internal Affairs was never told about allegations of drug- and money-skimming in the 4th District.

In addition, the ranking source said allegations a year ago about Caribbean Cruise tipoffs may not have been referred to Internal Affairs. Six months earlier, the internal unit had investigated similar charges but was unable to pinpoint any leaks.

"We are noted for our fair and vigorous investigations of police transgressions, and no blue veil of protection exists that would shield wrongdoers in our own ranks from accountability," Turner said at a news conference Aug. 27, the day The Washington Post disclosed the FBI investigation. "We stand ready to investigate any allegation of wrongdoing that is brought to our attention."

Whether or not Internal Affairs ever examined the allegations of skimming, the case that has emerged suggests that as many as a dozen officers knew about or were allegedly involved in skimming, and that a massive pattern of allegedly bogus warrants may have developed to support drug raids in the 4th District. U.S. Attorney Joseph E. diGenova, facing problems in prosecuting cases brought by the vice unit, last week decided to drop 300 to 400 such cases.

In citing the Internal Affairs Division's track record, police officials maintain that the office has played a role in the investigations of police wrongdoing as well as a number of cases involving public corruption in the civilian departments of the District government. Unlike internal units in many police departments, Internal Affairs has a mandate to investigate such public corruption. Among those cases:D.C. employment services official Crystal J. Willis, who pleaded guilty to a role in a purchasing fraud scheme. As an outgrowth of that case, information developed by the D.C. Inspector General and federal law enforcement authorities led to the successful prosecution of former deputy mayor Ivanhoe Donaldson. Basil Small, a procurement officer at D.C. General Hospital, who pleaded guilty to accepting a $2,500 bribe. Dennis Bethea, director of the office of emergency shelter and support services, who resigned in January 1986 after a contractor alleged that he extorted $1,000 in connection with a contract let by the D.C. Coalition for the Homeless, on whose board Bethea served. Bethea, who was not charged, has said that the money was a loan that he subsequently repaid. D.C. Council member Charlene Drew Jarvis (D-Ward 4), the subject of a current investigation into whether she used her official position to obtain business or bank loans for Woodrow Boggs Jr., a consultant who is her close companion and political adviser. No charges have been filed in the case.

In addition to the public corruption cases, the internal unit has acted in the cases of the former deputy chief of the 4th Police District, who received an official reprimand from Turner for mismanagement of the investigation that led to Operation Caribbean Cruise, and a lieutenant who was recommended for demotion for misuse of confidential funds in the same operation. The lieutenant's demotion is pending appeal to Mayor Marion Barry.

Notwithstanding these cases, critics contend that the department's performance in the arena of public corruption has invited federal intervention, which has led to an unprecedented array of continuing city government corruption probes organized under three separate federal grand juries.

"How can we have these kinds of allegations of corruption within the city system and not have anything, even in the way of a contribution, come out of {Internal Affairs}," said one longtime officer. "A legitimate question would be: Why does the federal government have to be in the forefront in the fight against local corruption?"

The answer most often given is that Internal Affairs is not an independent agency and is subject to the political control of the executive branch of the District government -- the mayor and the police chief. The only other local entity charged broadly with investigating corruption, the office of the D.C. inspector general, also reports to the mayor and, like Internal Affairs, is under no obligation to publish findings.

Because the District's unique charter includes no local prosecutor, state police force or attorney general, whistleblowers who do not have confidence in the Internal Affairs Division's independence have beaten a path to the door of diGenova. That is what happened in several major cases recently.

On July 16, two employes of the police department's drug screening program alleged in a letter to diGenova that police officials and ranking members of Internal Affairs tampered with drug testing procedures in at least one case where a police official's urinalysis tested positive for drugs.

In mid-August, Turner appointed an in-house panel of police officials to examine the allegations. However, on Wednesday, before the panel could reach any findings, the department relieved the two whistleblowers of their duties -- only to announce on Friday, after an inquiry from reporters, that the two had been reinstated.

"I find it ironic," commented Robert E. Deso, the police union attorney who drafted the letter to diGenova, "that the only action taken so far in this thing is against the people who gave information that initiated the investigation in the first place."

About a year ago, sources have said, police officers presented the chief and other officials with tape-recorded evidence that some 4th District vice squad members tipped off drug dealers to the Feb. 22, 1986, Caribbean Cruise crackdown. The operation, involving hundreds of officers, produced disappointing results -- only 27 arrests and seizure of less than $20,000 worth of drugs.

Sources have alleged that the police officers also told the police officials that some 4th District vice officers were stealing drugs and money seized in narcotics raids. Some time later, the officers concluded that the watchdog unit had not pursued the case, and they secretly brought the allegations of tipoffs and skimming to the FBI and U.S. attorney's office.

In doing so, the officers are widely perceived to have violated a taboo against taking complaints outside the department. According to a wide array of police officers and officials, Turner has clearly signaled that going outside the department with complaints of corruption will not be tolerated.

The message was vividly conveyed in the drug testing case and, four years ago, with the highly publicized transfer of Inspector Fred Raines, the head of the department's intelligence unit, who was reassigned to the post of night supervisor after he went to the Justice Department with allegations about Barry without first informing the chief.

The allegations involved unsubstantiated intelligence reports describing allegations that Barry had either used cocaine or was present while others used it during a 1982 Christmas party at This Is It, a nightclub on 14th Street NW that featured nude dancers. Raines said at the time that he went to the Justice Department because he was convinced that an outside investigation was needed, if only to show that such politically sensitive allegations would be thoroughly checked.

Barry, who acknowledged having been at the nightclub, denied ever having used cocaine or having been present when others used it and said the allegations were politically inspired.

"What happened with Fred Raines goes beyond the Internal Affairs Division," said Hankins of the Fraternal Order of Police. "He went outside the District government to the FBI and received the quickest and harshest punishment that I can recall anyone of that rank ever getting, and the message was very clear."

Raines had "lost his command, is the permanent night inspector and the subject of retaliation . . . ," Hankins added. "It had a chilling effect on officers departmentwide."

The story of Fred Raines is legend in the department, a symbol of the distrust for Internal Affairs and the taboo against going outside. There are two other cases that are frequently cited by officers and officials as examples of the department's unwillingness to police itself. The case of Inspector Winston Robinson, who while a captain in August 1985 was involved in an off-duty traffic accident while driving home from Turner's birthday party. Robinson tried to run from the scene and was apprehended and handcuffed by D.C. police officers after fighting with them a few blocks from his car.

Statements by police officers on the scene showed that Robinson had given officers a false name and was not carrying his service revolver, badge or departmental identification folder, as required of all D.C. police officers when they are in the District. Sources say that, although Robinson was placed under arrest for disorderly conduct, all documents of the incident that were made the night it occurred have disappeared.

The internal investigation of the incident was never given to Internal Affairs but was handled by Robinson's supervisor, Asst. Chief Carl V. Profater, who outranked the Internal Affairs commander, an inspector. Police sources have said it was highly unusual that Internal Affairs did not investigate the case.

The final investigative report on the incident sharply contradicted the sworn statements of officers on the scene and attributed Robinson's behavior to a severe bump on the head he allegedly received during the accident. Robinson said then that he did not remember anything that happened at the scene.

He was issued a $50 traffic citation, given an official reprimand and, seven months ago, was promoted to inspector. Robinson is now in charge of the department's urine-testing program. The case of Deputy Chief Sammie Morrison, currently head of the department's Office of Financial Management, who while a sergeant in 1973 was investigated by Internal Affairs and found guilty by a police trial board of failing to file federal and District income tax returns for the previous five years.

In 1983, Morrison was the subject of a separate Internal Affairs probe into alleged mismanagement of the department's $300,000 confidential fund, and the unit forwarded its findings to the U.S. attorney's office. A spokesman for diGenova declined to comment on the status of the case. Morrison has strongly denied misusing the fund.

A year later, Morrison received an official reprimand from Turner after Internal Affairs investigated an accident that occurred while Morrison was operating a police department boat for recreation while off duty.

In 1986, a grand jury investigated Morrison's arrangement to have a civilian employe of his office, who had been arrested and charged with first-degree burglary, released into his custody from the cellblock at D.C. police headquarters without first consulting the U.S. attorney's office. A spokesman for the U.S. attorney declined to comment on the case.

Morrison was promoted to captain in August 1982, to inspector in December 1985 and to deputy chief three months ago.