A smokey two-alrm fire caused extensive damage last night to the General Services Administration regional headquarters building in Southwest Washington, and sent toxic polyvinyl chloride fumes billowing 'through' through hallways.

Officials said two firemen and a building security guard were injured in the blaze, which was reported at 11:34 p.m. in the eight-story concrete building at 7th and D Streets SW.

About 100 GSA employes in the building were evacuated as firemen smashed open windows to vent the choking fumes. Efforts were under way early this morning to rid the building of any remaining smoke and fumes, but it was not immediately known how much of the building could be safely occupied today.

A large area of the fourth floor was heavily damaged in the blaze but no dollar estimate of the loss was available.

According to fire officials, the fourth floor, where it was believed the fire may have been smoldering for some time before being detected, was subdivided into many small offices, containing a variety of office machines and other electrical equipment. Insulation on the wiring in the equipment, which reportedly included one or more computers, produces polyvinyl chloride fumes when it burns, authorities said.

Heat, smoke and fumes, which spread to the third and fifth floors, hampered firefighters as did the building's intricate floor plan, authorities said. At one point firefighters without breathing masks were ordered evacuated.

One of the injured firemen suffered minor burns. The other two injured persons reportedly inhaled smoke or fumes.

Cause of the fire was not immediately determined.