One man was killed and another critically injured in Gaithersburg last night when their car collided with a police cruiser and slammed into a building, Montgomery County police said. Both men were thrown from the car, the driver into the building and the passenger into the cruiser.

The police officer who was driving the cruiser suffered minor injuries in the incident, which occurred about 7:30 p.m. at South Frederick and Cedar avenues.

The impact of the two men's Honda Civic punched a hole in the wall of a two-story building at 102 S. Frederick Ave., heaping bricks in the reception area of a real estate office.

Police said the Honda was northbound on South Frederick and the police cruiser, a Chevrolet Caprice, was southbound when the driver of the Honda tried to make a U-turn in front of the cruiser, which was not on an emergency call.

The officer driving the cruiser tried to avoid the Honda by changing lanes and attempting to stop, but struck the car broadside, police said.

Both vehicles continued south. The cruiser came to a stop in the 100 block of the street, but the Honda left the road and struck the building. It eventually overturned and came to rest against a utility pole.

The driver of the Honda apparently was hurled through a building window, police said. The passenger was thrown through the Honda's rear window and into the passenger side of the cruiser, police said.

The driver, identified as Jose Z. Canaza, 28, of West Deer Park Road in Gaithersburg, was taken to Suburban Hospital, where he was listed in critical condition. The passenger, Carlos Canaza, 17, of the same address, was taken to Shady Grove Adventist Hospital, where he died. Police said the two men were brothers.

The officer was identified as Darin C. Magee, 24, a member of the force for two years who is assigned to the Germantown station.

Speeds at the time of the collision were not known, police said. A spokeswoman said the speed limit where the crash occurred is 30 miles an hour.

Police said the officer was wearing a seat belt. It was not known whether the two other men were.

Charles A. Hayes, owner of the building that was hit, said the crash punched a five-foot hole in the wall and smashed a window.