Twins Phil and Steve Mahre, who won gold and silver alpine skiing medals in the Winter Olympics in Sarajevo this year, will introduce their championship downhill techniques in a series of six week-long classes at Colorado's Keystone Resort this season.

The classes, designed by the Mahres and their coach, Harald Schoenhaar, will be available to skiers of all ability, from beginner to expert. On at least one day of each week, one or both of the Mahres will ski with the classes and join in an evening discussion workshop.

Actual instruction will be provided by the Keystone ski school staff. A primary goal of the lessons is to help skiers develop their own natural skiing stance the way Schoenhaar helped the Mahres enhance theirs so successfully.

The Mahre Training Centers will be held Jan. 6-13 and 20-27; Feb. 3-10 and 17-24; and March 3-10 and 10-17.

The cost depends on the choice of accommodation, beginning at $718 per person double occupancy at Keystone Lodge, and includes seven nights' lodging, instruction, a six-day lift ticket, six breakfasts, six lunches and welcoming and graduation parties. A four-person condominium starts at $662 per person. The rate for children under 12 skiing with their parents is $366 each.

For more information: Keystone Resort, Box 38, Keystone, Colo. 80435, (303) 468-4242.

MEET THE AUSSIES: Seeing the whole continent is an awesome undertaking, so you might want to limit yourself to one region of Australia and get to know the people.

An organization called Bed and Breakfast Australia arranges stays for paying guests in private homes in the cities and at ranches and farms in the countryside. A brochure is available listing "Meet the Aussies" opportunities.

Within a morning's drive outside Sydney, for example, a number of working cattle and sheep ranches in the Quirindi-Liverpool Plains area take in guests. Horseback riding, hiking, fishing and swimming are among the recreational activities, and the guests join the ranch family for meals. A three-night visit, including meals, is about $190 per person; children under 12, about $145.

And though there is no guarantee, there's always the possibility in this part of the country that you will see a kangaroo.

For more information: Bed and Breakfast International (Australia), 18-20 Oxford St., P.O. Box 442, Woollahra, Sydney, N.S.W., Australia 2025.

FOR GOURMETS ONLY: A two-week truffle tour of Italy and France during the truffle-harvesting season, departing New York Nov. 29.

These special fungi, which grow underground on the roots of certain trees, are an expensive delicacy. The tour features truffle menus, truffle hunting with trained dogs and visits to truffle farms, processing plants and markets. On the itinerary are Rome, Florence, Umbria (for the white truffles of Italy), Monte Carlo and Perigord (for the black truffles of France).

Among the tour guides is Gary Lincoff, president of the North American Mycological Association, who teaches at the New York Botanical Garden. He has led study excursions to Asia and South America.

The cost of the truffle tour is $2,098 per person (double occupancy) for air fare, lodging, continental breakfast, motor coach travel and about half the dinners.

For more information: Educational Tours Inc., 5935 S. Pulaski Rd., Chicago, Ill. 60629, (312) 767-0477 or (312) 767-9076.

BARBADOS BY BICYCLE: Cycling is a good way to see the countryside, and why not a Caribbean island? A Washington firm, Chesapeake & Shenandoah Bicycle Touring, has scheduled a series of three eight-day cycling tours of Barbados this winter.

Accommodations are in beachfront hotels; cycling is in the cool of the morning with afternoons reserved for the beach or pool; and an accompanying van transports luggage (and any cycler who needs help over the occasional hill). The itinerary covers much of the island, with daily distances ranging from 14 to 35 miles.

Departures are Jan. 12, Feb. 9 and March 9. The cost is $795 per person (double occupancy) and includes lodging, breakfasts, six dinners and a shipboard dinner dance. Air fare is extra. Bring your own bike or rent one for $95. Helmet rental is $10. Each tour is limited to 18 participants.

For more information: Chesapeake & Shenandoah Bicycle Touring, P.O. Box 21002, Washington, D.C. 20009, 332-7166.

PLACES TO GO: About 700 of them, actually, detailed nicely in the 1985 edition of the Weekender's Calendar, an unusual guide to festivals, fairs and other events in the five-state area around Washington.

The 13-month calendar (it begins with December '84) is a day-by-day listing of such diverse attractions as Baltimore's Mardi Gras fest at Harborplace (Feb. 15); the "World Championship Wildfowl Carving Competition" at Ocean City, Md. (April 28); the Antique Aircraft Fly-In at Cambridge, Md. (May 19); and the Natural Chimneys Jousting Tournament in Grottoes, Va. (weekend of Aug. 16).

And since the calendar begins with this December, there's an extensive list of upcoming holiday events, including tours of historic houses in their yuletide finery.

The calendar sells for $5.95 and is available at Waldenbooks, Crown Books and other bookstores and shops. Included is a pullout section describing driving trips to 15 area destinations, including the region's vineyards, Charlottesville, Annapolis, Dover, Gettysburg and Philadelphia.

For the name of the store location selling the calendar nearest you: (703) 549-3385. The calendar may also be ordered from Andrik Associates, P.O. Box 5029, Alexandria, Va. 22305. Add $2 shipping for the first copy and 50 cents for each additional copy ordered. Sales tax of 24 cents for Virginia residents.

ACROSS THE BRIDGE: A guide map of Brooklyn, featuring 10 walking or driving tours through its distinctive neighborhoods, has just been released. It can be obtained for $1 (postage and handling) from The Fund for the Borough of Brooklyn, 16 Court St., Room 809, Brooklyn, N.Y. 11241.