The party's over but the calories linger on. A glance in the mirror will reveal why that second helping of Christmas pudding, the holiday goose and several dozen Christmas cookies are gone but not forgotten.

How sad it is that we must pay for our pleasures, but pay we must and, as the new year begins, it is either bread and water taken in solitude or planning parties that will restore us to our pre-holiday sylph-like selves.

The best party for our purpose is, unfortunately, totally dependent on the weather: a cross-country ski meet. Although it is not quite as restricted as downhill, with its dependence on lifts and the like, you still must have snow. The minute a good, healthy helping has been forecast, book a number of friends and (just as important) the skis to put them on. If you wait until the snow is knee-high on Massachusetts Avenue everyone else will have had the same idea and the stores that rent cross-country skis will be out.

Ski Chalet, 2704 Columbia Pike in Arlington, (703) 521-1700, rents the skis, boots and poles for $14 a day, Old Town Ski & Outdoors, 821 S. Washington St., Alexandria, (703) 683-1510, $14, plus tax, a day, and Potomac Ski & Sail, 3610 University Blvd., West Kensington, (301) 949-6800, $14 a day.

The tow path that runs along the C & O Canal is a perfect place to mush along, and if you make it all the way to Great Falls Tavern, there are blazed (though not maintained) trails for those feeling adventurous.

Bring along sandwiches and fruit in a backpack; cross-country skiing uses up lots of energy and will make everyone ravenously hungry. After all that exercise, it's okay to eat.

Ice skating is next on the list of good things to do when you're feeling fat and you can host a group indoors at the Fairfax Ice Arena, 3779 Pickett Rd., Fairfax, phone (703) 323-1131 for hours and prices, or outdoors at the National Sculpture Garden, 7th Street and Constitution Avenue NW, (202) 347-9041, or Pershing Park on Pennsylvania between 14th and 15th streets NW, (202) 737-6938. Both outdoor rinks charge $1.50 for skate rental and $2.75 for two hours on the ice.

If you'd like to plan an evening skating party, the rinks are open from 7:15 to 9:15 p.m. on Friday and from 7 to 9 p.m. on Saturday (call the rinks for other hours). The Sculpture Garden also has moonlight sessions on Thursday, Friday, Saturday and Sunday from 9:30 to 11:30 p.m., or, if your group is large enough to make it financially feasible, after 9 p.m. you can rent the entire Pershing Park rink for $75 an hour.

You also could glide along the Potomac, but check with the National Park Service, (202) 426-6700, first, to make sure you won't fall through the ice.

Another outdoor activity dependent on plenty of white stuff is a sledding party -- toboggans with people shrieking and hanging on tight so they won't slide off, or individual sleds borrowed from willing children while everyone tries to remember how to avoid shooting head-first into a drift. Battery-Kemble Park, on Chain Bridge Road off MacArthur Boulevard, has just the right hills for such tipsy-dipsy entertainment.

Now we come to parties that make it seem as though you've gotten lots of exercise when, in fact, all you've done is taken in a great deal of fresh air. Birding can use up a lot of energy if the bird has chosen to nest at the tip top of a mountain at the end of a perilous trail. But usually it hasn't, and exercise experts haven't bothered to calculate how many calories are used by the act of lifting binoculars.

But birding is an adventure and while you're out on the trail you won't be eating. Gather your fellow bird watchers at your house and then call the Audubon Society's Voice of the Naturalist, (301) 652-1088, to get directions for your wild goose chase. Not long ago, the voice would have directed you to places where harlequin ducks were flying about, or put you on the trail of the lesser black-backed gull, the greater white-feathered goose or a loon or an avocet.

Remember that though there are not as many birds around in the winter, the ones that are here are easier to see.

We now have arrived at the point where we substitute the pretense of exercise for exercise. A trip through the jungle would certainly knock off a few pounds, but that would take time and money and, given what lives in the jungle, might knock us off as well. So instead, we will call a convocation of fellow gardeners to join together for a trip through the U.S. Botanical Gardens at the foot of Capitol Hill between Maryland and Independence avenues SW.

There is mystery -- a ghostly white squirrel who darts among the jungle of trees -- and history: An ancestor of the Garden's breadfruit plant was part of a great adventure. When Captain Bligh sailed the Bounty toward Tahiti, he had on board plant collectors from Kew Gardens sent to search for the breadfruit. The mutiny put an end to that excursion, but the collectors eventually returned and pulled the plant out of paradise.

Now it is available to those of us who would like to pretend that when we stand in that steamy spot, surrounded by orchids and protected by 29,000 square feet of glass, we are not in Washington, D.C., but Tahiti.