Power was cut off to at least 30,000 Northern Virginia homes and businesses last night when part of a wooden pole carrying a 230,000 volt transmission line toppled, causing one of the largest blackouts in the area in some time, a spokesman for Virginia Power said.

The blackout, which began about 8:30 p.m., affected much of eastern and southern Fairfax County, particularly the Franconia area, as well as parts of Alexandria, Arlington and Prince William County, authorities said.

Power was restored to the entire affected area by 10:50 p.m., the Virginia Power spokesman said.

In calling the blackout one of the largest "in some time," the utility company official noted that the effects of storms are generally scattered widely over many neighborhoods, but that last night's failure was essentially concentrated in a single area.

The failure occurred when part of an 80-foot pole supporting the transmission line fell against another line, which ran parallel to it in the Hayfield area of Fairfax County. Contact between two conducting wires shut down the circuits, the Virginia Power spokesman said. It was not immediately known what caused the pole to break.

Fairfax County authorities said about eight houses were evacuated as a precaution in the area of the 6100 block of Bristol Way near where the transmission pole failed. Residents of the area reported seeing bright flashes and sparks, and the Virginia Power spokesman said it was feared that one of the power lines might snap, but they remained intact.