The house rules say you have to earn your gorp, so the children are hauling out their cross-country skis and stuffing plastic bags filled with the mixture of raisins, nuts and M&Ms -- purists use carob chips -- into their pockets as soon as we arrive at our rented log cabin at Herrington Manor State Park. Conditioned by the adult belief that snacks are immoral unless you're hiking, skiiing or otherwise expending energy, they are eager to hit the five miles of ski trails a snowball's throw from the cabin door.

None of the children -- Caroline, five, and Tabitha and Laura, eight -- has ever been on cross-country skis before, and all need a little help with their equipment. Tabitha and Caroline have children's cross- country skis whose cable bindings can be adjusted to fit any kind of boot, but Laura has adult-style gear -- light leather shoes whose fronts attach to the ski bindings and leave the heel free. The comfort and relative simplicity of cross-country equipment, compared to downhill equipment, is one of the great liberating aspects of the sport, and we are soon ready to take off into the woods.

Another liberating aspect is that you don't have to wait in lift lines and can take off when and where you please, although groomed and marked trails have obvious advantages. Ignoring them, we plunge into the woods, planning to pick up a trail our map tells us lies down the hill by the lake. Skirting the non-winterized cabins that are locked up for the season, we step over branches and skirt boulders poking through the snow.

"Just sit down if you get going too fast," I hear my husband shout to the children as they careen down a path not really meant for cross-country skis. "And wait until Laura gets out of the way."

Having climbed major mountains and done other wildly improbable things on skis, he now leads an improbable crew of three little girls who are first-timers and one lackluster skier in the advanced stages of pregnancy. I know better than to follow blindly in the tracks of a real athlete, and sidestep carefully down the hill; but the children follow his lead and receive a baptism of fire -- or ice. The abundant snow that covered Garrett County until recently had partially thawed and refrozen in icy ruts.

"It's not usually like this," I console my five-year-old, who greets the news in stony silence. She has fallen behind, and I am acting as rear guard, urging her on and trying to teach her the gliding motion that makes cross-country skiing easy.

"It's just like roller-skating," I tell her, but she eyes me skeptically.

"I wish I could go roller-skating instead," she ripostes.

older girls out onto the frozen lake, a flat but slippery place to ski. Tabitha falls and cannot get up without taking off a ski, which she carries to the bank far behind the others. Again the mopping-up action is left to the rear guard.

"Laura's supposed to be my friend and now she's skiing with Daddy," complains Tabitha.

Clearly, it's time for a gorp break, and we all gather at a picnic table beside the lake. While the children surreptitiously pick the M&Ms out of the trail mix and scatter the nuts and raisins to the chipmunks, the adults plot the course. The marked trail is an uninviting combination of slush and ice, so we stick to the woods, here a pine thicket where needles have replaced snow in many spots. Where the pines end, we come to a hill that leads to a wide meadow covered with a thick blanket of snow: a good place to practice.

The gliding, sliding action is facilitated by the fact that you can lift your heels without lifting your skis, but the children find it hard to master. Laura does a bit better, perhaps because of the adult-type skis. Tabitha and Caroline, although the cable bindings around their heels are loose enough, are perhaps psychologically inhibited by them and are still just trudging through the snow, a tiring activity. We stage mini-races and try to get the kids to coordinate pole and foot action. Although the techniques are never mastered, the terrain is easy and high spirits are regained. To keep spirits high enough for a second day of skiing, we decide to take off our skis and walk back to the cabin.

Laura's parents, delayed on their way, have arrived with her eleven-year-old brother, Ben, and as we sit around the wood stove eating, drinking and playing Othello that evening, we consider alternatives to the less- than-perfect cross-country conditions. Should we go to Wisp for downhill skiing on people-made snow? Should we check cross- country conditions at Blackwater Falls, about an hour away in West Virginia? Should we just curl up with our books?

As we breakfast next morning, however, snow starts to fall and we hurry to our skis to take advantage of it. Checking the map, we carry our skis across a road to a place where several trails begin. While we wait for Laura's father to check in with his office via the park phone booth, we practice some more. The children are beginning to get the hang of it and, encouraged, we hit the trail. The icy ruts are only partially dusted with snow, but there is room to manueuver around them. The woods are beautiful and quiet, inducing the peaceful, contemplative mood that cross-country skiing is supposed to induce. Even my five-year-old feels it.

"Mommy, do you think in heaven?" she asks.

The snow tapers off, then turns to sleet, a hard sleet that feels like hail pellets. We climb a hill, teaching the kids a modified herringbone technique aided by pole action, and then decide to take a shortcut. A wide swatch cut for a powerline leads down a hill to a trail that would cut about a mile from our trek.

Some of the adults, mindful that cross- country skis lack the edges that control downhill skis, hesitate at the top. But to the children, the wide hill is the great liberator. Ben and Laura, who have done some downhill skiing, traverse back and forth gracefully to the bottom. Tabitha and Caroline, whose forty-pound bodies build up no dangerous momentum, schuss the hill without falling.

"Come on, Mommy," they shout up at me. "That was really fun!" CROSSING INTO CROSS-COUNTRY There are cross-country ski trails suitable for novices at HERRINGTON MANOR (301/334-9180) and NEW GERMANY STATE PARKS (301/895-5453) in Maryland and at BLACKWATER FALLS STATE PARK (304/259-5511) in West Virginia. All have winterized cabins for rent, but most are booked well in advance. Accommodations are also available at a lodge at Blackwater Falls. Coming cross-country events include ski races at Herrington Manor State Park on January 30 and a cross-country ski tour of Savage River State Forest, also in Western Maryland, February 20, 21 and 22. The $50 fee includes food and lodging and reservations may be obtained by calling Maryland Forest and Park Services at 301/ 269-3761. The Audubon Naturalist Society's January cross-country ski trip is fully booked, but another trip may be scheduled in February. Old farm roads as well as state park trails are used and the group stays at a farmhouse near New Germany State Park. The fee of $82 for adults and $72 for children between 8 and 16 ($10 less for members) includes transportation, lodging, food and instruction. Call 652-5964. Cross-country skis, boots and poles are available for rent locally at Hudson Bay Outfitters and Appalachian OUtfitters. For ski conditions at Maryland parks call 301/768-0895. Blackwater Falls conditions may be ascertained by calling 304/259-5511.