The perennial pothole season has arrived early this year, and Washington area motorists are already axle-deep in pockmarked streets and those lesser road depressions that some black-humored highway officials like to call "surface distortion."

This week, what was once a surface distortion on the Maryland side of the American Legion Bridge at Cabin John grew into a "killer pothole" that could have done in a compact.

"It's the early snow, followed by the rain and, of course, the extreme ranges of temperatures," said Stan Ather, the District's chief street maintenance official, explaining why drivers are dodging potholes in winter instead of spring.

Yesterday, the city's Pothole Hotline (767-8527) was averaging 50 calls instead of the usual 10 to 20, and Ather ordered up 350 additional tons of cold-weather patching materials.

Area officials, grappling with the problem, were eager to discuss the birth of a pothole and to tell motorists how to avoid them -- and what to do if they can't.

"Rain is the real culprit," said Tara Hamilton, spokeswoman for the D.C. Department of Public Works. "The freezing and thawing expands the pavement, and once the water gets in and gets under the subsurface, you start getting that shifting that will make a pavement crack cave in even more, and create the infamous pothole."

There are two kinds of potholes, according to Marianne Pastor, spokeswoman for Virginia's Department of Transportation. The "deep pothole" of two inches or more "is what we really define as a pothole. Anything less is what we call a top pothole or surface distortion," when the moisture gets into layers of asphalt rather than under the base.

"We try to stay on top of them," said Pastor, no pun intended.

WTOP radio traffic reporter Bob Marbourg said he doesn't think this year's potholes are any worse, "but all you've got to do is hit one and you're in trouble."

When car meets road canyon, it can be expensive. Damage to tires, wheel rims or car suspensions can cost $25 to $870 to repair, according to the American Automobile Association's Potomac branch.

"Unlucky motorists who hit an unusually deep hole could have their oil pan ripped out," said spokeswoman Laura Martinez. She advised motorists to drive more slowly than usual on pothole-ridden roads and to apply brakes only if it can be done safely.

Mary Anne Reynolds, another AAA spokeswoman, said bridges often suffer the worst ravages of potholes. When it snows, she said, "we salt the heck out of bridges, and it seeps down and speeds up the cracking."

Maryland crews, she said, put a metal plate over one pothole on the American Legion Bridge at Cabin John Monday. But it came loose Tuesday morning, leaving a two-foot wide "compact car-eating pothole" that officials say tied up traffic for hours and caused a six-mile backup in Virginia.

Ather said the District received 8,000 calls last year and patched some 14,000 potholes. He said an aggressive road resurfacing program has cut the number of potholes from what existed a decade ago. Then, the city used up to 15,000 tons of asphalt a year; now Ather needs about 7,000 tons.

That's the good news. The bad news is that the real pothole season doesn't begin until March or April.