Shouting "Sell your coupons for cash," and waving fistfuls of $20 bills, a gaggle of self-styled hustlers beseiged passengers arriving at National Airport yesterday on Eastern shuttle flights from New York City in the lastest round of airline coupon mania.

The scruffy buyers were bidding furiously for the coupons -- good for half fares on most transcontinental flights -- that Eastern is handing out on its shuttles in a new giveaway that has spawned a rash of speculative fever up and down the East Coast.

"This is calm," said one travel agent who was in on the action at the Eastern exit ramp at National. "They're like animals in Boston and New York. It's a zoo up there."

Airline competition in the lucrative New York-to-Washington and New York-to-Boston corridor spurred this latest coupon giveaway, and an Eastern official in Washington estimated yesterday that the airline has handed out nearly 50,000 coupons since the promotion began Jan. 7. It's scheduled to end Jan. 31.

Passengers on most of Eastern's shuttle flights -- which cost $59 between Washington and New York and $56 between Boston and New York -- receive the coupons, which are good for a half-fare ticket on the transcontinental flights of most of the major airlines.On Eastern's New York-to-Los Angeles run, the coupon will cut anywhere from $175 from the price of a oneway night coach ticket to nearly $285 from a first-class ticket during the day.

Though Eastern is the only airline giving away the coupons, other airlines have jumped into the fray to accept them for discounts on their transcontinental flights. A traveler on American Airlines, for instance, could shave nearly $200 off the price of a one-way coach seat between Washington and Los Angeles.

The value of the coupons has set off a rash of speculative buying by everyone from ambitious college students to travel agents to ticket brokers, who go on to sell the coupons in huge chunks to corporations.

And despite the coupon's value on coast-to-coast flights, many of the shuttle passengers were in a selling -- and bargaining -- mood yesterday as they stepped off their flights from New York.

Cries of "How much you payin'?" and "No way, they're getting $50 each in New York," could be heard yesterday at National as the motley crew of buyers and the well-dressed passengers haggled with each other over price.

Few passengers seemed immune to at least toying with the idea of selling and one of the toughest bargainers was a woman in mink, carrying a Louis Vuitton bag, who finally flounced off when she couldn't get her price of $50 for the coupon. "I'll sell it when I get back to New York," she asserted as she left the shuttle area.

Still, some passengers weren't having any of it, and walked right past the shouting bunch of bidders without even a look. Former congresswoman Bella Abzug politely said "No, no, I'm going to use mine," as some of the men shouted, "Sell, Bella, sell," as she walked through the exit doors.

The coupons are potentially so valuable to corporations whose employes make coast-to-coast business trips that some companies have been buying up the coupons or, in the case of ABC News, ordering employes traveling on company business to turn them in.

A few of the coupon bidders, such as Jay Tepper of Brooklyn and a man who would identify himself only as "Tee from New York" have taken to flying continously back and forth on the shuttles and plying their trade on the airplane.

"I'm going crazy," said Second Officer Jim Walls on Eastern's noon shuttle from New York yesterday. "Guys are buying them right on the plane." sBut Walls said all the crew had done to stop the practice was ask passengers "not to be so over-enthusiastic about the coupons."

The giveaway, like a previous and much bigger coupon extravaganza sponsored by United and American last year, has spawned a complex business establishment. Besides the crew of hustlers at airports in Boston, New York and Washington, there are the travel agents and ticket brokers who are spending thousands to buy up the coupons in quantity.

James Dizon, sporting a camel's-hair blazer and black briefcase containing a bundle of cash, stood by quietly as his more aggressive cohorts hustled passengers for tickets yesterday at National. After all the passengers were gone, Dizon, the president of what he described as a major travel agency in Los Angeles, went around buying up the coupons in bulk.

For the little guys, said Dizon, "it's all a hustle and a gamble. The first in will win. The others will lose."