A three-hour standoff at a vacant Northwest row house ended last night when police searched the building and arrested a 15-year-old youth, who was charged with rape while armed, a D.C. police spokesman said.

Lt. William White III said the youth was arrested shortly before 11 p.m. inside the house at 1635 13th St. NW. White said that a shotgun and a revolver were recovered inside the house.

The barricade began shortly after 3rd District officers went to the address at about 7:40 p.m. in response to a reported sexual assault and robbery at the house, White said.

He said police were looking for "two to four" males who apparently forced their way into the building. At least one of them allegedly raped a 34-year-old Northwest woman there, White said.

The four also allegedly robbed the woman's companion, Oscar Davila, 41, of 5670 Seminary Rd. in Falls Church, of an unknown amount of money and a 1978 Ford automobile, White said. It was not known why the victims were in the house, he said.

The area bounded by 12th, 14th, Q and S streets was closed to traffic, and members of the D.C. police emergency response team entered the house at about 10 p.m., White said. They found the juvenile suspect on the second floor, he said.

Police then used tear gas in an attempt to flush possible additional suspects from the building, but they apparently escaped, White said. No shots were fired during the incident, he said, and no injuries were reported.

White said the arrested juvenile is to be arraigned today in the family division of D.C. Superior Court.

Police also arrested a 15-year-old Northwest youth and two adults at the scene in an unrelated matter, White said. He said Joseph Jennings, 50, no fixed address, Tyrone Fletcher, 21, whose address was not available, and the youth were charged with unlawful entry after police found them inside the building during the search.