Two D.C. police officers, arriving to back up a plainclothes officer Thursday night in Northeast Washington, apparently mistook him for an armed suspect and began shooting -- hitting their fellow officer, the murder suspect he was trying to arrest and a woman in the suspect's car, police said.

The officer and the suspect -- who police said was unarmed but was shot when he appeared to be fumbling for a gun -- were wounded, but survived. Odetta Emanuel, 33, who apparently was the only one of the three that the officers did not intend to shoot, was hit in the head and killed, police said yesterday.

The two 6th District officers who fired the shots have been placed on administrative leave with pay, as officials attempt to unravel what happened in a chaotic incident that has echoes of several shootings in the District, when D.C. officers wounded or killed their colleagues by mistake.

Police said the shootings took place about 8:15 p.m. at 49th Place and Blaine Street NE, in a pocket of neat single-family homes in the middle of one the city's most violent areas.

A police source said Investigator Joseph Gatling, 36, a member of the department's warrant squad, had received a tip that he could find William S. Wade, 26, who was wanted on a murder charge, in a house near that corner.

Gatling, in plain clothes and driving an unmarked car, went to the area and soon saw Wade get into the passenger seat of a car, according to the source. Gatling called for backup help, the source said, and officers from the 6th District responded, blocking Wade's car at the corner.

What happened next remained somewhat unclear yesterday, said Sgt. Joe Gentile, a police spokesman. Gentile's office released a statement saying that 6th District Officers Kevin Raynor and Antonio Long spotted Gatling and one of them "apparently mistook the plainclothes investigator for an armed suspect."

They yelled at Gatling that they were police officers and ordered him to drop his weapon, police said. The two officers then opened fire, hitting Gatling in the upper right thigh and Emanuel in the head, the police statement said.

According to the police statement, Wade, sitting in the front passenger seat, was believed by one of the 6th District officers to be reaching for a weapon. The officer shot him in the shoulder, police said. As it turned out, no gun was found, they said.

The police source provided a slightly different scenario, saying it was believed that the officers meant only to shoot at Wade and also struck Gatling and Emanuel by mistake.

D.C. Police Chief Charles H. Ramsey said yesterday that all officers are trained to give a secret signal so that other officers can identify them when they are off duty or working in plain clothes. Ramsey said police were investigating to determine whether Gatling had given the signal before Thursday's shooting.

Emanuel, who police said lived in the 1100 block of 13th Street NW, was pronounced dead at Prince George's Hospital Center about 10:40 p.m. She had worked as an executive assistant at George Washington University since late last year, the university said.

Wade, of the 2600 block of Evarts Street NE, was arraigned yesterday in D.C. Superior Court, charged with one count of first-degree murder while armed. Magistrate Judge Andrea L. Harnett ordered that he be held with no bond pending a preliminary hearing Friday.

Prosecutors allege that Wade shot Thierry Jocelyn Nkol early Aug. 7 in the 3000 block of 11th Street NW. According to an arrest warrant, witnesses said Wade fired shots from a car at 11th and Irving streets NW.

Wade has been unemployed for at least the past year and lives with his mother, according to court papers filed yesterday. He has prior convictions on drug charges.

Long, 25, has been on the police force for three years, officials said. Raynor, 33, is a 12-year veteran. He has been involved in at least one previous gunfire incident. In 1995, Raynor told The Washington Post that he fired at but missed a gunman who shot at him during a chase.

Officer-on-officer shootings plagued the department in the 1990s, including two in 1995. Off-duty officer James M. McGee Jr. was fatally shot by an officer on duty in February 1995 while trying to arrest two robbery suspects at gunpoint. In December of that year, plainclothes Detective Lani Jackson-Pinckney was shot by a fellow officer while she was trying to thwart a carjacking. Jackson-Pinckney, who was pregnant, survived but was left with some paralysis; her unborn child was unharmed.

In July 1998, one off-duty officer fatally shot another, Thomas F. Hamlette Jr., after Hamlette took out his service weapon during a dispute outside a D.C. nightclub. Hamlette's family later got a settlement of more than $1 million from the city.

All of the 1990s cases involved white officers shooting black officers. All of the officers involved in Thursday night's shooting are black, police said.

Police investigate the shooting at 49th Place and Blaine Street NE, where two officers wounded an officer and a suspect and killed a woman.