Pickpockets thrive at holiday time in busy shopping malls, says Officer Mike Neal of the Montgomery County Police Department's crime prevention section.

They often target shoppers exiting jewelry stores, carrying unwieldy bundles and riding escalators. "Whenever you get bumped in a crowd," he says, "immediately check your wallet."

One of the newest ploys at stop lights and in shopping center parking lots: "Someone opens the passenger door, grabs the purse or packages lying on the front seat and takes off."

Among Neal's other Christmascrime deterrents:

* Carry little cash and only the credit cards you need. Keep in an inside pocket, close to your body.

* Discard boxes from expensive new merchandise cautiously. "So your trash can doesn't tell the world you've got a new TV or computer." Cut up boxes and/or hide them in opaque, secured garbage bags.

* Lock all car doors. Place packages in the trunk and leave purses on the floor, not the seat.

* Avoid large pocketbooks. Women tend to set these down while shopping. If you must carry a purse, pick one with a zipper covered by a flap and carry it toward the front of your body.

* Keep your wallet in an inside front pocket. If you must put it in your rear "sucker" pocket, button it in.

* Never flash cash. If you carry a money clip, keep small bills on the outside and larger ones inside.

* Lock your house even if you are just slipping next door for eggnog. "The vast majority of burglaries are committed by neighborhood kids."

* Ask neighbors to check your house and pick up mail and newspapers if you'll be out of town. "Canceling service tells more people you're away." Have neighbors reset automatic light timers every few days to go on and off at different hours. Be sure they know where you can be reached.

* Tape your home address and instructions for calling emergency services by each telephone. "Nothing is more helpless than an out-of-town guest who doesn't know how to call for help."

* Get a security guard if you see someone suspicious in a parking lot. Most large stores and malls have uniformed or plain-clothes guards who may escort you to your car.