First came the chair on a cable, called a lift, then day passes and skis with metal edges. Next came bindings that released, boots that buckled, pants that stretched and "cats" that groomed.

Now it's the foursome, or "Quad." And, as much as any industry development, this one is changing skiing.The quad is a four-place detachable chairlift. What makes this lift so different, however, is not the numbers but the speed. The quad is two times faster than the newest high-speed double or triple now running up ski slopes. It is, said one rider, "a jet among props (propeller-driven planes)."

Skiers can, in less time, get their runs in on the slopes. They can ski hard, change, and then be on with their vacations.

Actually, quads are not new - the first was built in Breckenridge, Colo., in 1981 - but are just being discovered. As of January, there were 48 in the United States, most from Colorado east. At Colorado resorts alone there were 23 quads, six of them at Vail. The consensus is that before too long, quads will be as common at ski areas as triple lifts are now . . . Skiers will expect them. Those areas without quads will be passed over by ski vacation planners.

Presently, there are no quads in Utah. One is scheduled to be built at Solitude this summer.

The only area in the Northern Rockies - Utah, Idaho, Wyoming and Montana - with the new higher-speed quads is Sun Valley, also first to introduce the chairlift to the world 53 years ago.

After two years of looking, planning and studying, three of the detachable quads were installed this past summer and opened in November. One of the quads, the Challenger, runs on the Warm Springs side of Mount Baldy from bottom to top - 9,057 feet with a vertical rise of 3,144. It is the highest vertical rise of any chairlift in the country.

New lifts were needed to replace older lifts on the Warm Springs side of the mountain. Also, better bottom-to-top access was desired.

According to Tim Silva, assistant mountain director at Sun Valley, the Challenger cut travel time from bottom to top by more than two-thirds . . . "Where it used to take 30 minutes and two different lifts to get to the summit, now skiers can get to the top in less than 10 minutes," he said.

Cost of the three quads, said Wally Huffman, general manager of the Idaho resort, was nearly $7 million, "which is a lot more than other lifts, but the added expense was worth it. There's a lot of interest in quads.

"I think it goes with the trend. There are far fewer seven-hour-a-day skiers around today. Not even the locals are skiing seven hours a day. Today's skiers want to ski three or four hours, then go on to something else. Quads are symptomatic of what's going on in the industry."

By riding the quads, skiers can get all the skiing in they want, or that their bodies can take, within three to four hours.

"The rest of the day is spent doing other things . . . shopping, cross-country skiing, ice skating, resting, or whatever they want," said Huffman.

Silva noted that earlier this year one of the die-hard locals attempted to outlast the quad. The legs, Silva said, gave out before the lift closed. "He skied about 94,000 vertical feet (about 30 runs or more than 50 miles) and couldn't go anymore." One western ski area gives special recognition to skiers who can ski 100,000 vertical feet in a week.

In operation, the lifts look no different than standard lifts. The seats are wider, but without other lifts for comparison, the speed doesn't seem too excessive.

Where standard chairlifts run at between 450 and 500 feet per minute, however, quads typically run at 850 and can run up to 1,000 feet per minute.

Another difference is at pickup and dropoff points. Chairs are held onto the cable by a "grip." As the chair approaches the lower wheel, the grip releases and the chair moves onto a second, slower-moving cable. The chair gently and comfortably picks up skiers, four at a time, then is brought up to cable speed before the grip reattaches to the cable. At the top, the chair leaves the cable and quickly slows to a very comfortable exit speed.

"The thing we've found," said Huffman, "is that skiers are excited about the quads. It's like when jet planes were first introduced. People arranged their schedules in order to fly the jets. We've found skiers arrange their skiing in order to ride the quads.

"Another thing we've noticed is that once people ride the quad it becomes the standard. They don't really notice the quads being that much faster. To them it just seems like the conventional lifts are going that much slower."

A second quad at Sun Valley parallels the Challenger but ends at mid-mountain. The third is on the east side of the mountain, beginning at the Roundhouse, and takes skiers to the summit.

The three quads have a total capacity of about 6,500 skiers an hour, and increases Sun Valley's total hourly capacity to 24,644 skiers.