The birds have defied almost every tactic that Chevalier has used to scare them away from the runways, where they pose a potentially disastrous hazard to planes landing and taking off.

Inflatable owls didn't do the trick - they just provided the gulls with convenient perches. And the peregrine falcons that Chevalier introduced seemed to prefer tastier birds.

The cannons that fire ear-splitting blanks and the trucks that blare gull distress calls from loudspeakers proved to be minor annoyances to birds that were used to the roar of jumbo jets.

"They seem to get accustomed to the deterrents pretty easily," said Chevalier, who supervises seven airport employees whose full-time job is to harass the gulls.

And so the laughing gulls - which are named for their shrill call and which are smaller than common gulls - have proliferated.

Well, the gulls aren't laughing now.

This summer, Chevalier and company blasted 15,000 of them from the skies.

A team of U.S. Department of Agriculture wildlife biologists used shotguns to teach the gulls a simple lesson: an airport runway is a dangerous place for feathered fliers.

"We called it a re-education program," said Jack Gartner, the manager of aeronautical services for the airport. "But apparently, they were not as smart as we thought they were."

By the time their guns fell silent in August, the biologists had killed more than half of the adult laughing gulls believed to nest in the Jamaica Bay Wildlife Refuge, a federally protected marshland next to the airport where the gulls have multiplied exponentially in the last decade.

Airport officials said the heightened "harassment" campaign at least brought temporary results. The number of collisions between birds and aircraft during the laughing gull nesting season dropped from 155 last year to 53 this year. The nesting season lasts from May through September.

"We're not the black-hat marauders of wildlife," said Richard A. Dolbeer, a USDA biologist from Sandusky, Ohio, who headed the hit squad. He said the 80-day shoot was justified by the threat that the birds posed to aircraft and passengers.

"The bottom line is that something had to be done," he said. "It's not a situation that could be ignored. In my opinion, it's just a matter of time when a real tragedy occurs there."

The biologists were astonished that the gulls did not act like ducks or geese, which learn quickly to avoid hunters. The gulls behaved like kamikazes and continued flying over the runways, even though the USDA hunters stood in the open, wearing bright orange vests and firing at will.

"They just didn't seem to show any fright response," Dolbeer said.

Biologists will not know until next spring, when the laughing gulls return from their winter migration, if the birds learned any lasting lessons. The bird population may well return to this year's levels because so many laughing gulls are migrating to New York from New Jersey, where refuges are overpopulated.

But it is unlikely that this summer's harassment will solve a problem that has long plagued Kennedy Airport, whose busy runways in southern Queens lie next to a thriving marsh that is part of the Gateway National Recreation Area.

The National Park Service, which manages the wildlife refuge, says it is aware that birds pose a threat to aircraft. Nationwide, bird strikes were responsible for 38 accidents between 1982 and 1989 that caused seven deaths, according to the National Transportation Safety Board.

But Park Service officials say they are bound by their legal mission to protect the very birds that the airport wants to exterminate.

"The Park Service feels the very last solution should be going in and damaging the population of the laughing gulls," said Robert Cook, a natural resources specialist at the Park Service.

That position has led to numerous clashes between naturalists and aviation officials, who view birds and aircraft as incompatible.

Park Service officials say the Port Authority of New York and New Jersey, which owns the airport, has not worked hard enough to make JFK unattractive to the birds. But airport officials say they've spent hundreds of thousands of dollars cleaning up garbage, improving drainage and letting the grass grow long to make the area less hospitable to gulls.

"We keep doing all these things, but the birds keep flying over, around and through the airport's airspace anyway," said Gartner.

Airport officials had hoped that recent closure of two landfills near the airport would reduce the volume of gulls. Indeed, great numbers of herring gulls and black-backed gulls have moved to Staten Island, where they can feed at the city's largest landfill.

But the laughing gulls were unaffected by the closing of the landfills because they feed mostly on marine life and insects.

Last year, under pressure from federal aviation officials, the Park Service reluctantly allowed the airport to take its war against the laughing gulls into the protected marshes.

The Park Service supervises an experiment to destroy about half the laughing gull eggs in the marsh. Biologists suffocated the embryos by coating the eggs with mineral oil.

But Park Service officials said the egg-oiling experiment was a failure. And they have vowed to block any other efforts by the airport to enter the refuge without first obtaining an environmental impact statement.

Airport officials have been acutely aware of the danger of bird strikes since 1975, when an Overseas National Airways DC-10 ingested a flock of gulls as it sped down a runway. An engine stalled, fell off the wing, and started a fire that destroyed the plane. The 140 passengers escaped.

Most of the 300 or so bird strikes that occur each year at JFK cause little damage. But since 1979, the airport has attributed 42 aborted takeoffs to bird strikes. Those collisions damaged or destroyed 37 engines.

"Over the years, I've seen the damage they can cause," said Chevalier, a lean man with spiky white hair who has worked at JFK since 1957, when it was called Idlewild Airport.

While Chevalier showed a visitor around the airport last month, he could not have asked for a more dramatic demonstration of the destruction that a bird can cause. As he stood next to JFK's Bay Runway, watching a United Airlines 747 bound for Tokyo picking up speed to take off, the huge plane's engines suddenly sighed and it turned off the runway.

The radio in Chevalier's yellow pickup truck crackled as the control tower called for the bird-control unit to scan the runway - the United pilot reported that he had struck a bird. Chevalier sped off to the tarmac.

"It was a bird strike, all right," said Chevalier, returning to the truck with a handful of fresh feathers.

Back at the gate, mechanics looked over the grounded plane. The impact of the bird had mangled the metal turbine blades inside one of the 747's engines. United officials decided to replace the engine and delayed the flight overnight while they flew in a new engine from Seattle.

The total cost for the repairs and overnight lodging for 241 passengers: $250,000.

"That just shows you what one bird can do," said Chevalier.

Chevalier sent the remains he collected from the runway to the Smithsonian Institution, which identified the bird not as a gull, but as an immature male peregrine falcon - an endangered species.

"I hated to see that," said Chevalier, an amateur ornithologist who spends his vacations banding waterfowl at wildlife refuges.

Most of the time, Chevalier's relations with birds are benign. He loves to watch the egrets, osprey and herons that teem in the marsh near the runways, but seem to know better than to stray onto airport property. The laughing gulls, which first reappeared here 12 years ago after nearly being wiped out in the 1800s by hunters seeking feathers for women's hats, don't show the same intelligence.

And Chevalier has a special contempt for gulls.