FRANKFURT -- President Ronald Reagan sleeps on it, former President Lyndon Johnson slept under it and Charlemagne never switched castles without it. And now, to the sorrow of waterfowl everywhere, down bedding, the age-old hallmark of central Europe, is rapidly becoming a global phenomenon.

What the rest of the world is currently waking up to is a pillar of daily life in Mitteleuropa. On any given morning throughout German-speaking countries, federbetten, as the comforters are called, can be seen being aired from countless bedroom windows. Dawn in Deutschland is a goose's nightmare come alive.

"About 92 percent of all German households own some kind of down or feather comforter," said Dieter Volker, the president of Frankfurter Bettfedernfabrik Fritz Volker GmbH in Frankfurt, the leading West German manufacturer of processed down and feathers, as well as bedding.

Although few other nations even approach West Germany's fanaticism for feathers, foreigners in growing numbers are slumbering in the ethereal, sweaty warmth of down.

"Export sales, particularly to the United States and to a lesser extent Japan, have been rising dramatically over the past few years," said Torben Busekift, chief spokesman of Northern Feather Group International in Copenhagen, the world's largest producer of down bedding.

That waxing appetite has also sparked a scramble for position in the U.S. market among the world's down bedding manufacturers. On Feb. 16, Northern Feather made a "very friendly" bid to acquire all the outstanding shares of Chatham Manufacturing Co. of Elkin, N.C., for $46 a share in cash, valuing the company at $77 million, Busekift said.

Northern Feather posted profit of $15.5 million in 1987 on sales of $230 million, Busekift said. The company now runs five factories in the United States, all built in the past 10 years.

Volker also has first-hand knowledge of the jockeying in the U.S. market. In October, Scandia Down Corp. of Seattle bought the Frankfurter Bettfedernfabrik, founded by his family 103 years ago, from the West German Quelle mail-order group.

Tom Reichman, president of Scandia Down, said the opportunity was too good to pass up.

"The Germans are absolutely excellent at making down bedding," Reichman said. "It's like Coca-Cola; no one else has ever been able to exactly duplicate them. Nearly 90 percent of the machines used to process feathers and down and clean them after they have been in use come from West Germany."

Reichman is an entrepreneur who took over Scandia Down in 1980 after he saw "a market niche that was going to grow." The company now has 80 retail outlets across the United States, with five more under construction.

"In 1980, about 6 percent of U.S. households owned some type of down comforter," said Reichman, who has slept under one since childhood. "That's up to about 11 percent today and it's rising."

Annual sales of Scandia Down are about $30 million and have been steadily climbing, he added.

The price of a down comforter depends on the type and amount of down or down and feathers used to fill it and the covering, which is generally cotton. Most comforters are made to customer specifications. At Scandia Down, prices range from about $250 to $1,200, Reichman said.

In Europe, prices can run even higher, Volker said. "The most expensive down is eiderdown, from the eider duck," he said. "Some of the comforters can cost 3,000 or 4,000 marks. Its insulating qualities are extraordinary. This duck is found only in northern Canada, Greenland, Iceland and northern Scandinavia and, unlike the other birds used for down, it's not slaughtered. In fact, eider ducks are strictly protected because the duck itself plucks the down from its breast to line its nest. When nesting season is over, the eggs have hatched and the ducklings have left the nest, then the down can be collected."

Most of the down and feathers used in West Germany come from Eastern Europe, primarily Poland, Hungary and Czechoslovakia, Volker said.

But when and how the warming down and feathers were first put into bedding is anybody's guess.

That warmth, in any case, is the reason for down's modern-day allure, according to Irene Ollinger, who has sold down comforters for the past 15 years at Betten Ollinger in Frankfurt.

"There is simply nothing as comfortable," she said. "They conform to your body and they absorb the moisture that we give off in our sleep. There is nothing else, natural or synthetic, that gives you so much warmth for so little weight. It's not the down which warms you, but the air that is trapped between the thousands of tiny particles of down."

The "moisture," which Volker said amounts to 200 grams per night, is generally given off in the form of sweat and is the reason down comforters must be aired every morning.

While some people are not partial to waking up in a sweat, some well-known historical figures appear to have been devotees. Legend has it that Charlemagne, the eighth-century king of the Franks and later emperor of the West, who like most conquerors was frequently shifting headquarters, always took a well-stuffed feather comforter along on his travels.

"Even if that's not true, it's still a great legend," Volker said. In more modern times, down bedding may have been one of the few things Ronald Reagan and Lyndon Johnson ever had in common, according to Busekift.

"We know that President Reagan sleeps on a Northern Feather down pillow and that President Johnson slept under one of our comforters, because we still have the orders they placed," he said.