You know how cold it can get in Washington in winter.

Picture yourself stepping outdoors into a frosty wind this morning, stripping quickly to a swimsuit and plunging into the gray Potomac River for a swim. Alexander L. Mottola of New York did just that last February for the new Cher movie "Suspect." On most winter weekends, he's likely to be found taking a chilling dip -- or two, or three -- in the Atlantic Ocean off Coney Island near his home.

Mottola is longtime president of the famous Polar Bear Club, a small, but hardy bunch of cold water/cold weather enthusiasts. You may think they are crazies, but, says Mottola, the Polar Bears are a very friendly sort who welcome company in their rigorous pastime. You are invited to join them.

Every Sunday in winter, just before 1 p.m., Mottola and his group gather at the Coney Island lifeguard station on the Boardwalk at the foot of Stillwell Avenue to prepare for their swim. Show up with a swimsuit beneath your overcoat, and you will be considered one of the gang. So the thermometer has slipped to freezing and snow has been falling for hours. It's all part of the fun of cold weather.

"We go in snow, rain and hail," says Mottola. "That doesn't bother us." Sometimes as a demonstration for spectators, he will break up the ice in a lake and go for a plunge. The crowd on shore gapes in astonishment. "Their mouths are wide open. When I'm in the water, all I can see are their cavities."

A romp with the Polar Bears is one of the many outdoor adventures awaiting travelers who wouldn't rather stay home and nap beside a fire. You can book a tour that will enable you to set foot on the North Pole, try snowmobiling in Iceland, go cross-country skiing through the Canadian wilderness or watch real polar bears -- they are the ones wearing the heavy fur coats -- in their natural habitat in far northern Norway.

But more about those other Polar Bears, the nearly naked ones whose exposed skin turns a bright, tingling red when they emerge from the sea. "Beet red," says Mottola. "When you submerge, you get the blood circulating. It's nature's way of warming you up." How do they stand it? Why do they do it?

A swim in the chilly Atlantic is not really so uncomfortable as it seems, says Mottola, a retired office machine dealer who at 73 has been a Polar Bear for more than 30 years. "I tried it, I loved it, I became addicted." But first you have to psych yourself up to want to go in. That's part of the preliminaries at Coney Island.

Once the Polar Bears have assembled on the beach in their suits -- they have changing rooms and lockers at the lifeguard station -- Mottola leads them in calisthenics. The exercise builds an esprit de corps while keeping everyone at least minimally warm. "Then I blow the whistle," he says, "and we all go in at the same time." It's a quick dip, maybe 30 seconds or so, with a lot of whooping and hollering.

You don't have to completely submerge to qualify as a Polar Bear. "Just up to the neck," says Mottola. Afterward you might expect everyone dashes for a towel. Nope. These aren't softies we're talking about here.

"None of us carries a towel," he says. The cold, dry air does the job instead. "We dry off automatically."

According to Mottola, the winter swimmers don't find the water especially cold. This is because their bodies first become adjusted to the outside air, which may be chillier than the water. Air temperatures can drop well below freezing, but not water, which of course becomes ice. "When you come out, you're warmer than when you went in."

Mottola looks on his weekly ritual as a way of maintaining good health and as a form of relaxation. "Our members do not catch cold. I can probably outrun most fellows half my age. When I get home after a swim, I'm so totally relaxed." And hungry, though he eats a hearty breakfast before he heads for the beach.

Over the years, the Polar Bears have been called upon to practice their particular pastime for other than recreational purposes. Mottola and five other Polar Bears appear in an opening sequence in the movie "Suspect," a murder mystery set in Washington starring Cher as a lawyer and Dennis Quaid as a Capitol Hill lobbyist. The Polar Bears are first seen jogging. Next the camera catches them removing their shoes alongside the Potomac at Georgetown. And then in they go, only to discover a floating body. The plot is set.

Mottola says he had to take two dips into the Potomac for the brief but important sequence. "The first time I dove in by mistake, and somebody yelled 'cut.' " When he got out, the director wrapped him in a robe, and other crew members dried his swimsuit and his hair so he could take the plunge all over again with the cameras rolling. "We got paid as stunt men. They {the film company} pay very well."

Founded in 1903, the Polar Bear Club has about 40 active members, most of them from the New York area but several from around the country and abroad who join in a swim when they are in the city. A few other clubs in frosty regions of the country are affiliated. There are about equal numbers of men and women who are members. The youngest is 12 and the oldest is 86. For membership information or details about the next dip in the Atlantic, contact Mottola at 376 Naughton Ave., Staten Island, N.Y. 10305, (718) 979-8370.

Among other available cold-weather adventures:

Flight to the North Pole. For a brief period in April, weather and sunlight conditions are just right to land a ski-equipped plane at the geographic North Pole. For 10 years Skip Voorhees has been flying small groups of travelers to the top of the world. This year's six-day excursion departs April 3 from Edmonton, Alberta.

First stop (by jet) is Resolute Bay, Canada's gateway to the High Arctic in the Northwest Territories. The tour continues on by Twin Otter aircraft to Eureka, a weather station on the west coast of Ellesmere Island. One night each is spent at Eureka before and after the flight to the North Pole. After a 600-mile flight over the polar ice cap, the tour group has about 30 minutes to walk about the North Pole and take photographs.

From Eureka, the tour heads for the Inuit settlement of Grise Fiord on the south coast of Ellesmere Island, where, says Voorhees, Inuit guides are "anxious to show outsiders their frozen homeland." Among the options, you can help build your own igloo and sleep in it; go snowmobiling up the face of a 2,000-foot glacier for a view across the frozen sea; or take a ride in an Inuit sled. The price from Resolute Bay is $7,000 per person. Contact: Special Odysseys, P.O. Box 37, Medina, Wash. 98039, (206) 455-1960.

Polar bear watching in Norway. Only 170 miles from the North Pole, the Norwegian archipelago of Spitsbergen is home to thousands of polar bears. The 12-day trip departs April 20 during the period when the bears are emerging from their inner-island denning areas and heading for the permanent ice pack. Daylight lasts more than 20 hours at this time of year, which means plenty of opportunities for photographs.

From Oslo, the tour flies to Longyearbyen, the principal town on Spitsbergen. Then participants climb aboard snowmobiles for the ride to a special base camp for a three-night stay. Lodging is in isothermal tents designed for Arctic cold. The cost from Spitsbergen is $1,990. Contact: Mountain Travel, 1398 Solano Ave., Albany, Calif. 94706, (800) 227-2384 or (415) 527-8100.

Snowmobiling in Iceland. A typical ride takes snowmobilers over Iceland's snow-covered lava fields, up the slopes of extinct volcanoes, past cascading waterfalls and through valleys dotted with natural thermal pools. Of course, there's time out for a midwinter dip. In the warm and steaming water, you can pretend you are a Polar Bear vacationing in the Caribbean.

Departures are every Saturday from New York, Feb. 13 through April 23, on Icelandair. The price for a six-night package is $1,439 per person (double) for air fare, meals for four days, lodging, transfers and use of a Ski-Doo snowmobile. Contact: Decker's Sno-Venture Tours, P.O. Box 1447, Eagle River, Wis. 54521, (715) 479-2764.

Cross-country skiing in Canada. There you are sitting in a woodlands sauna in a ski camp in Ontario's Algonquin Provincial Park, about four hours by train north of Toronto. Too hot, you think. Well, just open the door, advises a brochure from Canadian Wilderness Trips, and take "a dive into a snowbank. The truly courageous can try the icehole." This is country to tempt any Polar Bear.

The tour firm offers three- and four-day cross-country skiing trips from now through March 18, departing Toronto Thursday or Friday almost every weekend. The trips are open to beginners as well as experienced skiers.

Base camp is at Kawawaymog Lake just outside the northwest corner of Algonquin Park. Skiers travel old logging roads, the well-groomed South River community trail and other private but less-groomed trails. With so much snow around, you can build a snow hut, go snowshoeing and try your hand at snow sculpture.

Groups range from about eight to 20 skiers who stay in a wood-heated sleeping cabin, described as cozy, with bunk beds and storage space. A second cabin serves as kitchen, dining room and lounge. Hardy skiers who want privacy can opt for a canvas prospector tent, a hand-built snow hut or the open sky.

The price from Toronto is about $155 (U.S.) for a three-day trip and $185 for a four-day trip, depending on the rate of exchange. Contact: Canadian Wilderness Trips, 187 College St., Toronto, Ontario M5T 1P7, Canada, (416) 977-3703.