Scores of motorists woke up yesterday to find they had been frozen out of their cars because of the unusual weather that struck the Washington area -- a punishing combination of heavy rainfall followed by a sudden plunge in temperature.

Local motor clubs and auto service centers said the complaints about frozen car doors, windows and locks began about 6 a.m. and did not slow down until nearly noon, when sunshine and higher temperatures temporarily solved most of the problems.

"We had 200 or 300 calls of that type by noon," said Joe Logan, director of automotive services for the local American Automobile Association (AAA). The calls for help -- which came in addition to the usual calls about flat tires and dead batteries -- kept AAA telephones busy and service trucks rolling throughout the morning.

The unusual weather conditions were caused by the arrival of an intense cold front, which blew in late Wednesday accompanied by gusty wind and rain, the National Weather Service said yesterday. In one hour, the temperature dropped 24 degrees -- from 65 degrees at 6 p.m. Wednesday to 41 degrees an hour later.

"Normally the drop would be about 10 degrees an hour when a front goes through," said forecaster Jerry Harrison."

Temperatures continued to drop during the night, reaching a low of 17 degrees between 6 a.m. and 7 a.m. Thursday morning -- about the time that the calls for help began to reach AAA dispatchers.

"When moisture gets into the car lock and then freezes, you can insert the key but it may not open," Logan said. Moisture seeping into the area around the door or around the window may also freeze, making it impossible to get into the car.

Two solutions, Logan said, are:

Warm the frozen area with an electric hairdryer.

Spray the area with a commercial de-icer.

Logan cautioned against heating the key because it might break off in the lock if the key is made of aluminum. He also warned that pouring hot water onto frozen windows could shatter or crack the glass.

The most typical cold-weather problem for motorists, however, is the battery malfunction, Logan said. "Cars require more cranking power as temperatures drop, so cold weather brings out the worse in the electrical system," he said.

Motorists are less likely to have battery problems if they keep terminals and cables clean. "If they are corroded, the electricity won't flow . . . even if the battery is operational," he said.

Yesterday, many motorists did not have a chance to check out their batteries because they couldn't get into their cars to try to start them.

Pat walbridge, who lives near Dupont Circle, trudged three blocks throught the cold to her car and inserted the key into the door lock. Nothing happened.

"I tried heating the key with a cigarette lighter but it still wouldn't open," she said. Walbridge then walked three blocks back to her home and retrieved a can of de-icer spray. That didn't work either.

"I left the car there and just walked to work," Walbridge said.

Other Washingtonians, meantime, were struggling with gasoline tank locks that had frozen shut.

"They would come in to buy gasoline and then we couldn't get the lock open to pump in the gas," said Bill Mason, whose son-in-law owns the Old Dominion Shell, 4400 Old Dominion Dr., Arlington. Mason said station attentants overcame that problem.

"We keep a hairdryer here [in the service bay] and we used that on car locks," he said.

Finally, there were some cases in which motorists successfully pried open their car doors but then could not shut them.

"One man drove in here with the door half open," said Tom Reidy, owner of Reidy's Exxon, 9331 Georgia Ave., Silver Spring. Reidy had the man's car -- a Plymouth station wagon -- brought into the enclosed service bay where it was warm and where station attendants could spray the door with a de-icer. After a few minutes, the car door had been thawed sufficiently to shut properly.

No more rainfall is expected for several days, according to the Weather Service. The forecast is for clear, cold nights and sunny days. By Saturday the warming trend is supposed to push the temperatures back into the 40s.