Federal investigations into civil rights abuses by police officers -- including dozens of probes launched in Prince George's County in the past two years -- rarely lead to prosecutions, Justice Department records show.

From 1991 to 1998, federal prosecutors weighed the results of about 17,000 investigations into whether police officers, prison guards and other law enforcement agents abused their police powers. But prosecutors filed charges against only 252 people, convicting 159, according to Justice Department records obtained by a research group affiliated with Syracuse University.

In Maryland, the FBI has conducted more than 200 civil rights investigations of law enforcement officials in the past decade.

Only two of those cases have resulted in indictments. One led to the conviction last week of a Prince George's police officer who turned a police dog loose on a homeless man.

Some lawyers and local prosecutors criticized the FBI and Justice Department for raising false hopes among victims' families, given how few officers are charged with depriving someone's civil rights under "color of law."

"They give you the appearance that, 'Uh-oh, here comes the big, bad FBI. Watch out,' " said Jack B. Johnson (D), the Prince George's County state's attorney who has prosecuted several county officers in state court for misconduct. "But I haven't seen any results. They have not helped us out on this. We've stood alone."

Federal authorities defended their prosecution rate, saying it is extremely difficult to convict problem officers.

They said that juries are generally willing to give police the benefit of the doubt and that good officers are reluctant to testify against colleagues who cross the line. At the local level, Johnson has characterized the lack of cooperation from police as a "blue wall of silence."

Moreover, federal law requires prosecutors to prove not only that officers acted illegally, but that they did so willfully and intentionally.

"They are difficult cases," said Albert N. Moskowitz, chief of the criminal section of the Justice Department's civil rights division. "We have to prove that an officer acted with a bad purpose to violate someone's constitutional rights. It's a pretty high standard."

Said Bill Lann Lee, who headed the civil rights division at Justice during the Clinton administration, "These cases are a remedy of last resort because the standard of proof is very high." When federal authorities do decide to prosecute, Lee said, "it's essentially for those outrageous cases that state authorities can't or won't handle."

The FBI is regularly asked to examine allegations of police brutality, including recent high-profile cases in Los Angeles, New Orleans, Cincinnati and New York.

But one of the busiest places for federal agents has been Prince George's County. Since April 1999, the FBI has announced 33 criminal investigations into possible civil rights violations by Prince George's police officers, with 11 of them opened in the past two months.

The majority involve allegations of excessive force, including shootings and beatings. Three cases focus on whether the police department's homicide unit deprived suspects of their constitutional rights by subjecting them to lengthy interrogations that resulted in false confessions.

The Justice Department is conducting a separate examination of the county's police department to determine whether a widespread pattern of excessive force or racial discrimination exists. That probe is a civil matter and could result in a lawsuit to force the department to change its practices.

The investigations coincide with increased scrutiny of Prince George's police, in part for their unparalleled record of using deadly force. From 1990 to 2000, Prince George's police shot and killed more people, per officer, than any large law enforcement agency in the nation.

Peter A. Gulotta Jr., an FBI spokesman in Baltimore, said federal agents typically send their findings to the U.S. attorney's office in Maryland and the Justice Department's civil rights division. Federal prosecutors then decide whether to file charges, he said. "We don't make any determination on that," he said.

Prosecutors almost always drop the case, citing weak evidence or a lack of criminal intent, records show.

Many cases are declined after only a cursory review.

For instance, federal prosecutors in Maryland closed almost 60 percent of the FBI's civil rights investigations from 1991 to 1998 after spending less than an hour reading the case files, according to the Justice Department statistics.

In the past decade, only two FBI civil rights probes of local law enforcement officers in Maryland have resulted in indictments and convictions.

In March 1998, Prince George's Cpl. Timothy J. Moran pleaded guilty to beating a handcuffed man with his nightstick.

And Wednesday, Prince George's Officer Stephanie C. Mohr was convicted of violating the civil rights of an unarmed homeless man by releasing her dog on him in September 1995. Prince George's Sgt. Anthony Delozier was acquitted of conspiring with Mohr.

It was the second trial in the case after jurors deadlocked in March. In a plea bargain, a Takoma Park officer pleaded guilty to being an accessory after the fact.

Despite the low number of prosecutions in Maryland, Acting U.S. Attorney Stephen M. Schenning said his staff puts a high priority on civil rights probes.

"We look at these cases closely and take them very seriously," he said.

The FBI has opened 45 civil rights investigations of Prince George's officers since 1995, said Royce D. Holloway, a police spokesman. He said the outcome of those cases -- only two led to indictments -- reflects well on the department.

"We hope it helps reinforce to the community that police officers have done the right thing in these cases," Holloway said. "It shows that an outside, unbiased agency has reached the same conclusion that the department has."

Several attorneys and relatives of victims of alleged police brutality complained that FBI and Justice officials are too quick to accept the police versions of events.

In 1993, the FBI investigated the death of Archie Elliott III, a 24-year-old Forestville man who was shot to death by officers while he was sitting, handcuffed, in the front seat of a patrol car. Police said he was reaching for a gun in his pocket that he had concealed during a search.

The dead man's mother, Dorothy C. Elliott, said she had high hopes for the federal investigation at first but grew exasperated when the FBI waited months to examine local police reports instead of conducting an independent review.

"It's very frustrating," she said. "Whatever the findings are by the local people, that's what they go with."

Last month, Justice Department officials announced that they would not bring charges against the Prince George's officer who shot Prince C. Jones Jr., a Howard University student who was followed for 15 miles by an undercover agent and killed in a case of apparent mistaken identity.

The FBI spent several months examining the case. But an attorney for Jones's mother said federal investigators were slow to interview witnesses and reluctant to pursue leads.

"The FBI investigations are disingenuous and phony," said Ted J. Williams, who has filed a civil lawsuit in the matter on behalf of Jones's mother. "They will announce to the public that they are going to conduct an investigation, knowing full well that they aren't going to prosecute the police officer."

Approximately 2,500 investigations into alleged abuse of civil rights under color of law are referred to Justice officials each year.

From 1991 to 1998, federal prosecutors sought indictments in 1.5 percent of the cases presented to them by the FBI and other agencies, according to Justice Department data obtained by the Transactional Records Access Clearinghouse, a nonprofit research center affiliated with Syracuse University.

John R. Dunne, an assistant attorney general for civil rights from 1990 to 1993, said federal prosecutors pursue only "extreme cases" that are buttressed by clear and convincing evidence.

For example, he said the Justice Department probably would not have pressed charges against two Los Angeles police officers who were convicted of beating motorist Rodney King if there had not been a videotape of the 1991 incident. "It was clearly a fluke," he said. "It's very rare that you find fair, objective evidence of guilt."

At the same time, Dunne said the tiny percentage of civil rights investigations that wind up in court suggests that many law enforcement officers are getting away with breaking the law. "In my mind, there's no question about it," he said.

James P. Turner, a deputy assistant attorney general in the Justice Department's civil rights division from 1969 to 1994, said one reason for the low prosecution rate is that the FBI does not closely screen civil rights complaints before opening an investigation. He said federal authorities don't want to dismiss the cases out of hand, even if the vast majority go nowhere.

"The very act of opening an investigation shows there is some higher authority and serves as an informal way of communicating to the public that these laws exist," Turner said. "When the FBI shows an interest in a case, it can stir things up even if it ends up not being prosecuted."

Prosecution rates are low across the nation, with almost one-third of U.S. attorney's offices failing to prosecute any officers for such violations from 1991 to 1998.

The most aggressive was the Northern District of Mississippi, which prosecuted 18 local law enforcement officers out of more than 600 cases received from the FBI.

John R. Hailman, chief of the criminal division in the U.S. attorney's office for northern Mississippi, said the key to a successful prosecution is persuading upstanding officers to testify against fellow officers, something they are often reluctant to do.

"It's very tricky and sensitive," Hailman said. "You have to have an investigator and a prosecutor who can talk to the officers, so they know you are pro law enforcement. If they believe you and trust you, they will work with you. You can't be a rookie."