A thunderstorm drenched parts of the Washington area with an early two inchs of rain yesterday afternoon and knocked out electricity for more than 12,000 Virginia and Maryland homes.

The most rain fell in the Largo area of Prince George's County. The National Weather Service recorded 1.85 inches there.

The storm blew into the western soburbs at 2:30 p.m. and passed across to the east by 4:30 p.m. It left one-half to two inches of rain in its path, but no serious flooding was reported.

Initially, 10,000 Potomac Electric Power Co. customers in Montgomery and Prince George's counties were left without electricity and numerous traffic light in the Bethesda-Wheaton-Rockville [WORD ILLEGIBLE] were knocked out. Service had been restored to 4,000 of these coustomers by early evening, but a Pepco spokesman said some of the others in the region between Potomac and Largo would bot have power until this morning.

In Virginia, about 2,000 North Arlington residents lost their electricity as the storm hit. Service was restored shortly thereafter, according to the Virginia Electric and Power Co. A few scattered outages remained.

Minor flooding was reported in low-lying regions of Fairfax County.

Temperatures of National Airport dropped from 88 to 76 degrees during the storm. Today's temperatures are expected to range between 84 and 88 degrees. Humid weather, a chance of afternoon and evening thunderstorms and highs around 90 degrees are expected Thursday through Saturday.