Until a few months ago Air Florida was the cut-rate flight to the future of the airline business, a 9-year-old high flyer that used cheap seats and Green Stamps to teach the old established lines how to compete for riders.

One of the first small airlines to realize that deregulation of air service would revolutionize air travel, Air Florida in the last four years has grown from a $21 million-a-year operation that never flew outside of Florida to a $350 million international air carrier.

Flying mostly used airliners with nonunion crews, Air Florida drew jeers from the big carriers when it offered S&H Green Stamps on some flights, but attracted so many passengers that other lines were forced to match its low prices.

Air Florida was growing so fast that in August a company official boasted that, "if our present rate of growth were to continue, in five years we'd be the biggest airline in the free world."

Barely a month later, the trouble began.

First, Chairman of the Board C. Edward Acker, who got most of the credit for Air Florida's success, was lured away to try to save the ailing giant Pan American World Airways. Then the slump in air travel caused by the recession and the air controllers strike forced the airline to lay off 100 headquarters employes. Finally on Wednesday, an Air Florida flight slammed into the 14th Street bridge and crashed in the Potomac.

Air Florida was so new to the business that it had never had an accident before, let alone a fatal crash, and by some accounts was unprepared to deal with disaster. "We never lost a passenger," a stunned Cesar Alvarez, senior vice president and chief spokesman, said after the plane went down.

Reporters were kept waiting for more than two hours Wednesday afternoon for an Air Florida briefing on the accident and the airline was still struggling yesterday to respond to inquiries about the crash. Some victims' families complained that Air Florida officials remained in Miami, but others praised the airlines decision to arrange a special flight for the next of kin.

Airline crashes rarely have a serious impact on an airline's business, industry sources say, but the psychological effect could be felt by the young carrier.

The crash had far less impact on Air Florida's stock than the departure of Chairman Acker last September. In over-the-counter trading yesterday, the first orders came in at 50 cents a share less than the day before but by midafternoon Air Florida Systems Inc. stock was back to $6.25 or $6.375 a share, the same as on Wednesday.

When Acker left, however, the stock was selling for $17. "You can tell the day he announced he was going just by looking at the price of the stock," said one Florida broker.

It was Acker who took a struggling little intrastate airline that had never made any money and turned it into a formidable competitor on the busy runs up and down the East Coast.

Air Florida founder Eli Timoner made his money in the candy business and in 1972 started an airline to fly back and forth from Miami to points in central, northern and western Florida. The big airlines weren't interested in short-haul flights and Air Florida quickly built its business up to 150,000 passengers a year, but lost money every year.

The line's fortunes changed in 1979 when the federal government began lifting regulations, taking away the exclusive rights of lines to fly interstate routes and opening up fares to competition.

Business doubled that year--to $21 million--and the company began to make money, a $2.4-million profit. Total revenues for 1981 jumped to 17 times the the 1979 level to $350 million and Air Florida made $13 million in the first nine months of its fiscal year.

Air Florida now flies to London, Costa Rica, Honduras, Venezuela, Jamaica and more than a dozen U.S. cities. The original planes have been replaced by a 30-plane all-jet fleet.

Some of its planes are used craft -- the Boeing 737 that crashed here was bought from United Airlines--but eight new 737s and three of the new 757 models have been ordered.