If, while you are driving home from a Christmas party tonight, you see flashing lights and a "Batmobile" in your rear-view mirror, it may be because you have had too much to drink.

This holiday season, from 9 p.m. to 4 a.m. on weekends, two roving breathalyzer-and-testing vans -- the "Batmobiles" -- and police in six scout cars will roam the city to detect drunk drivers and turn them over to the vans for processing.

On any given Saturday night, said Capt. Wayne Layfield, commander of the D.C. Police Department's traffic enforcement branch, one out of 10 cars on the road will be driven by someone who is drunk. When the holiday season culminates next week on New Year's Eve, he estimated, "one out of 5 drivers will be drunk."

Layfield has ordered a double shift for New Year's Eve: there will be police vans and cars operating from 4 p.m. on Dec. 31 to 8 a.m. on Jan. 1.

Those New Year's Eve arrests will bring the District of Columbia's 1981 total of drunk-driving arrests to approximately 4,000, Layfield estimated. Of the 50,000 traffic fatalities every year in the United States, about half are alcohol-related, according to the National Highway Traffic Safety Administration.

Drunk driving is a criminal charge and a first conviction can result in loss of license, a fine or imprisonment.

"We were only making about 900 arrests a year back in 1972," Layfield said. Before the police department began using mobile testing vans, he said, it took a police officer about 6 1/2 hours to "process" the arrest: that is, to read the offender his rights, carry out the testing and then complete the pile of paperwork that accompanies all police activity. Many officers felt that their time could be better spent in other pursuits, said Layfield, a 19-year veteran of the D.C. police force. "It used to be, if you were out on patrol, you'd hear of a drunk driver and head the other way," he said.

By 1980, he said, the processing time was "less than 30 minutes." But, he warns, even though the number of drunk-driving arrests quadrupled during the last few years, the problem is far from solved. "For every drunk driver arrested," he said, "there are 2,000 who aren't."

Sober drivers can protect themselves from those 1,999 drunk drivers who are not stopped by giving them a wide berth on the road. George Reagle, director of the National Highway Traffic Safety Administration's office of driver and pedestrian programs, recommends that drivers learn some visual cues that police officers use to detect drunk drivers:

* Surveys of drunk-driving arrests have found that the chances are 65 in 100 that a driver taking an unusually wide turn will be legally intoxicated -- that is, have a "blood-alcohol content" of .10, or one-tenth of 1 percent of total blood volume.

* There is a 60 percent chance that a car drifting back and forth across a lane marker is piloted by someone who is drunk, and a 30 percent chance that someone who has forgotten to turn his headlights on at night is "DWI" -- the police abbreviation for "driving while intoxicated."

* Other cues listed in the National Highway Traffic Safety Administration's "DWI Detection Guide" include straddling the center of the road or a lane marker (65 percent), almost striking an object or vehicle (60 percent), driving more than 10 miles per hour below the speed limit (50 percent) and braking erratically (45 percent).

Reagle was quick to point out that protecting against drunk driving is not just a matter of being careful on the road. "If you're at a party and you can see a friend is drunk," he urged, "take his keys and drive him home, or call a cab, or let him sleep overnight." Reagle's colleague John Moulden advised holiday drivers to watch themselves as well. "Don't drink on an empty stomach," he said.

Layfield had another bit of advice: "If you have to drink, know your limits."