One man was injured and about 20 families were displaced from their homes last night when a fire that authorities said was caused by arson sent clouds of smoke billowing through corridors of a high-rise apartment house in the White Oak section of Montgomery County.

Fire officials said the blaze was apparently set in an elevator at The Point apartments, at 11200 Lockwood Dr., and caused damage estimated at $350,000. Most of the damage in the building near the intersection of Rtes. 29 and 650 was confined to the elevator, parts of its shaft, and associated equipment, they said.

The fire was reported about 9:30 p.m., authorities said, and when firefighters arrived they found the burning elevator stopped in its shaft on the 10th floor of the 20-story building. They said smoke filled the 10th floor and spread to upper stories.

Many residents of the building fled down stairwells and assembled outside as firefighters quickly brought the blaze under control. Authorities said smoke and limitations on elevator service caused residents of about 20 apartments to be displaced. A Red Cross representative was reported on the way to the scene to aid in relocation.

The man who was injured hurt an ankle when he jumped from a third floor balcony. Fire officials said he was taken by ambulance to Holy Cross Hospital.

The method by which the fire was set was not reported immediately. One source said combustible materials were found in the elevator. Fire investigators remained on the scene late last night.