INSTRUCTOR Dietmar Tannheiser addressed his half-frozen class in a warm German accent. "Smile," he said, "Skiing is fun."

Smile, skiing is expensive," quipped the lady behind the cash register.

One of the first lessons any novice skier learns is that skis, boots, poles, lift tickets, lessons, transportation, clothes, lodging, and Chapstick can run through a few hundred dollars faster than Jean-Claude Killy can run a slalom course.

But this year a group of novice skiers from the Washington area discovered that the lady behind the cash register can be circumvented, at least temporarily, and that Dietmar Tannheiser is always right.

For $80 per person, the 75 novices signed up for five Friday nights of skiing with lessons, lift tickets, equipment rental, transportation and leadership all thrown in. The program is offered by the Montgomery County Recreation Department at Ski Liberty near Gettysburg, Pa. Rita Howard, who runs the program for the county, said it was developed for people to find out if they like skiing without having to invest in their own equipment.

"The program lets people try out skiing, supplemented by expert lessons, for only a minimal amount of money," she said.

At 5:30 p.m. on Friday the novices, ranging in age from 8 to 55, left by bus from the Cabin John Tennis and Ski Shop. They were on their first trip together, so their expectations were varied.

"This is going to be hilarious," chortled Christy Curry, 21, of Bethesda, one of the group leaders. "We're all beginners and everyone is going to be on his rump. That's how I'll keep track of them all."

"I think I'm gonna do ick," predicted third-grader Debbie Allamong of Washington.

"I've never been near skis before," said William Curtis, 10, of Gaithersburg. "I don't know how I'll do, but I'm looking forward to learning how to get up. It's supposed to be a lot harder than falling down."

The ride was a little over an hour to Ski Liberty and pandemonium - the resort handles several hundred beginners on Friday nights. "We understand better than areas the special problems of beginners, and I think we are well organized to meet their needs," said Jean Richter, who manages the resort with her husband.

The instruction started immediately. First came the boots, heavy and stiff for ankle support.

"If the buckles on your boots do not face outside, then you have them on the wrong feet," announced the video screen. Very basic.

Then came the skis. They are selected according to the height of the skier, but all the skis are very short. Liberty teaches "GLM" - the graduated length method of instruction - which starts all beginners on short skis.

"GLM is the most favored method of instruction," explained Gary Nett, head of the ski school, to one Potomac girl looking down at her waist-high skis. "Shorter skis are easier to handle and learn on. Later you will work up to longer skis as your skiing improves."

After the safety release bindings were adjusted to the weight of each skier, the video screen took over again and ran through the routine of how to put skis on. The instructors divided the slipping and sliding masses into groups of seven to 10. Though the temperature was about five degrees and the wind gusted to 30, nobody complained.

Some shivered, and the first thing instructor Bob Horowitz taught was, "if your buns get cold, do this." He jumped up and down. "Keeping moving keeps you warm." Half the class jumped around.

In each group the instructor demonstrated proper stance.

"Hands in front, knees bent, leeean forward; you should just be able to see your hands in the bottoms of your eyeballs when you're looking straight ahead."

The instructors then proceeded through traversing the slope, elementary turns and stopping.Safe and controlled skiing was emphasized. A fence has been erected around the beginners area so that more experienced skiers couldn't come schussing through the neophytes and rattle them.

After about 45 minutes on the gentle slope of the beginners' area, the classes were ready for the chairlift and the easier slopes on the rest of the mountain. Several members of Tann heiser's class looked skeptical. It's a long way up the mountain.

"I'm not going up there; I haven't done anything right yet," blurted one beginner.

Tannheiser had anticipated that and took his class aside.

"All you have to do is sit in the chair, keep your tips up as the chair lifts you off, and keep your tips up when the chair puts you down. Don't forget to lower the safety bar after you get on, and don't forget to raise it before you get off. If you have trouble, a man up there will stop the life. When you get off, the person in front of you might have fallen. Try not to hit him."

Getting on the double chairlift went smoothly, Getting off was a little rougher.

At the top of the lift is a short, steep grade. After leaving the chair each person had to slide down the grade in order to get our of the way of the chair he left behind. At the bottom of the grade was a tangle of skiers frantically trying to separate themselves from one another before another skier came sliding in, usually falling down to stop. The other the skiers just kept piling off the lift.

"Fridays nights are always a zoo up here," said a lift operator as he grabbed one fallen skier after another, pulling them to the side. he knew what he was doing. Nobody got hurt and only rarely did he have to stop the lift.

Tannheiser soon gathered up his pupils and eased them toward the slope. While the rest of the class waited, he took the girl who had been afraid of the lift and cautiously led her down the slope. The process was repeated for each beginner until the class was together again. With successive short distances traversed successfully, each skier gained confidence.

When Doug Nebert, 14, of Bethesda, had made it part way down the slope, he happily announced, "skiing is not so complicated after all." Mary Jakoby, a housewife from Potomac, agreed and added that it was "romantic."

Barbara Show of Wheaton kept wanting to go faster and faster and always ended up falling. "I love it," she announced from the ground.