An object that workers in a Tysons Corner building used to prop open a door was discovered yesterday to be a pipe bomb, forcing the evacuation of about 50 people from the seven-story building.

Police took the bomb from the building at 8027 Leesburg Pike and disarmed it on a safety range near Dulles International Airport.

John Lerch, a technician for the Chesapeake & Potomac Telephone Co., said he reported for work yesterday at the building and he spotted the doorstop outside a utility room.

"It's one of those things where it's obvious it's a bomb, said Lerch. "I said: 'This is a bomb.' "

Lerch said he called Fairfax County police, who X-rayed the object and determined it was a live bomb.

Police said the first two floors of the building were evacuated. A spokeswoman said the bomb appeared to have been controlled by a radio receiver similar to that on model airplanes.

Lerch said he learned that a worker unknowingly had found the object behind some drums, tossed it down a hallway toward the utility room and later used it for a doorstop. Leach said the worker was stunned when he told him what he had kicked down the hallway. "You're kidding?" the worker said.