An undercover D.C. policeman who was trying to arrest a drug suspect in Southeast Washington was mistakenly shot and seriously wounded last night when other officers arriving at the scene opened fire on him, authorities said.

According to D.C. Police Chief Maurice T. Turner Jr., two 7th District officers, dressed in casual clothing, arrived at the scene and failed to recognize that the man with a drawn revolver, Ricky Graham, 25, also in old clothes, was a fellow officer.

An account given late last night by Turner, but described by a police spokesman as necessarily sketchy, said it was Graham's own radio call for help that brought the two officers to 25th Street and Minnesota Avenue SE about 9 p.m. and led to Graham's being shot in the abdomen and left thigh.

Graham, a member of the force for less than a year, was taken to Washington Hospital Center where he was listed early today in serious condition. Sources said he was not wearing a department-issued bulletproof vest.

The incident appeared to be the first of its kind in years involving D.C. police. Authorities said they recalled a similar incident more than 15 years ago in which a plainclothes officer pursuing a suspect near Stanton Park in Northeast Washington was mistakenly shot and killed by a police sergeant who failed to recognize him as a policeman. Subsequently, plainclothes and undercover officers began wearing certain items of clothing so that other officers might more easily recognize them.

Investigators continued interviewing witnesses to the confusing incident for hours, and by early this morning full details still were not known.

In the account given by Turner in a news conference outside the hospital center, the incident began when Graham was trying to make an arrest for an unspecified narcotics violation. A fight broke out and Graham called for help on his radio. The first officers who reached the scene were Sgt. David P. Davis and Officer Larry Cauley.

"When they responded they didn't recognize Officer Graham," Turner said. The officers were part of a tactical team. Such teams are often used in undercover operations and in crime prevention work. To go unrecognized by criminals they wear no uniforms or badges.

In his brief statement, Turner said that when Davis and Cauley arrived at the far Southeast intersection, they saw a man with a drawn revolver and heard shots.

At that point, Turner said, the two officers fired. He said that Graham was hit twice, but Turner did not make clear which officer's shots wounded him.

After Turner's preliminary statement, a police source supplied additional details. The source said the incident began when Graham and a partner were attempting to make an arrest, and Graham became involved in a scuffle with unruly bystanders.

According to the source, Cauley, 37, a member of the force for 15 years, and Davis, 33, a member for 12 years, saw a man with a gun and one of them fired two shots. Graham fell, with his revolver still in his hand, and was ordered by the other officer to drop the weapon, according to the source. When he failed to do so, the other officer fired, the source said.

Police said a Southeast Washington man was arrested on a drug charge in connection with the incident at the intersection.

Police said Derrick A. Jones, 20, of 4810 Alabama Ave. SE, was arrested and charged with possession with intent to distribute PCP in connection with the incident at the intersection.