Screenwriters and cartoonists often cast bird-watchers as timid eccentrics in funny hats with Sibley guides sticking out from their safari jackets and binoculars around their necks. The perfect disguise for a terrorist, perhaps?

But serious ornithologists tend to have a bit of Indiana Jones in them. Ned Brinkley, for one, has driven into hurricanes looking for birds blown off course to unusual places. He has floated through swamps searching for evidence that the ivory-billed woodpecker is not extinct. And he was not about to knuckle under meekly when he learned that officials worried about terrorism were about to ban visitors from the Chesapeake Bay Bridge-Tunnel, one of the best birding spots on the East Coast.

Ever since the attacks of Sept. 11, 2001, Americans have grown accustomed to probes into their private lives and a great many new restrictions. From full-body searches at airport boarding gates to barricades around the Capitol, the nation has accepted many intrusive and prohibitive security measures as the price of safety.

Bird-watchers are oddly vulnerable to the new scrutiny. They carry binoculars, scopes and cameras. They like to go to such places as buffer zones around military bases and nuclear power plants, where lots of birds roost. They are sometimes turned in to police by suspicious passersby.

This time, Brinkley and a few cohorts were prepared to fight back. Their successful effort to regain access to the bridge islands illustrates how it is possible to continue their activities, even in a security-conscious age. But it requires concessions that once would have been considered extreme. It is a predicament many Americans are facing.

Today, the commission overseeing the span is scheduled to vote on a compromise negotiated with the bridge's executive director and head of security. Under the plan, scientists and researchers would be allowed to go on the islands that connect the bridge once they get a pass, renewed annually. Amateur bird-watchers would have to submit to a security check several weeks in advance and pay $50 an hour for a police escort.

"Why allow people whose intentions we don't know [to] dictate how our lives as Americans, our lives as Virginians, our lives as bird-watchers, are restricted?" asked Brinkley, who runs a bed-and-breakfast in Cape Charles when he is not leading bird-watching tours.

"It's patriotic to question bureaucratic decisions that impinge on our liberties. Are we vigilant or cowards? Are we creative, or passive and lazy?"

Their success also illustrates that bird-watchers have friends in high places.

They conferred with security experts who have worked for places that know a thing or two about counterterrorism tactics -- the Pentagon, State Department, United Nations, airports and nuclear power plants. They boned up on threat scenarios involving biological weapons and researched padlocks and high-tech ID cards. They offered to undergo criminal background checks and take crime-watch training.

"At some point, you have to choose between your lifestyle and increasing your security," said Tim Travan, a former U.N. weapons inspector in Iraq who advised the bird-watchers on counterterrorism issues. "If you give up too many civil rights and have too-draconian security, what exactly is it you are protecting?"

The Chesapeake Bay Bridge-Tunnel, a 17.6-mile span that costs $17 round-trip for a passenger car, connects Virginia's Eastern Shore with the mainland at Virginia Beach. The entrance and exit of two tunnels in the middle of the bay are secured by small, man-made islands of granite boulders. At the southernmost island, there is a restaurant and a fishing pier open to the public.

The three northern islands are popular with bird-watchers. The authority that operates the bridge has courted birders with ads in premiere ornithological journals. Bird-watchers consider it a special place to observe up to 350 species of birds, like being on a ship in open water.

Until this year, visitor passes were handed out almost casually. A mailed or faxed request routinely secured a letter of permission granting access to the islands for a year.

That changed after a risk analysis by the state Department of Transportation. It warned that the air-intake buildings providing ventilation to the tunnels were prone to sabotage, said Steven M. Mondul, state director of the Office of Security and Emergency Management. Homeland Security authorized a $1.3 million grant to secure the ventilation.

The report triggered a rethinking of the entire approach to security. Last year, 800 letters of permission were handed out to birders who provided little more identification than a driver's license. The authority concluded that it had not screened visitors well or kept tabs on their movements. Allowing the public, even bird-watchers, was a potential threat.

"Everybody knows that post-9/11, we can't do anything like we did before," said Clement M. Pruitt, head of the bridge's police force. "Anybody who can fly planes into the twin towers can find ways to circumvent our rules."

No one questioned the need for more security on the bridge, located just north of the largest Navy base on the East Coast.

"We believe this is in the top 100, if not the top 20, terrorist targets in America," Brinkley said. "We accept their assessment of the threat."

Short of a specific threat, however, many wondered if the ban accomplished its intended purpose. Why keep the southernmost island, with its restaurant and pier, open to the public? Why allow fishing boats to approach? And would a fence around the ventilation buildings really keep out a determined terrorist?

"We've all come to realize we're living in a different world," said Mitchell A. Byrd, an ornithologist at the College of William and Mary who has been observing birds on the bridge since it opened in 1964. "Some of our rights, like the total freedom of movement to do what you want to do, are compromised. The issue is, to what purpose?"

Many wondered what might be sacrificed next.

"If this would help protect this great land of ours by giving up part of a privilege, I would do so willingly," said Alice Wheeley, a real estate broker who has been an avid bird-watcher for 40 years. "But you kind of wonder, if you give up one privilege, how many more are you going to give up, and why?"

In April, after hundreds of bird-watchers had mailed in objections, the bridge authority offered an alternative plan. There would be no annual permits; groups would be admitted by prior arrangement. And they would have to pay for an off-duty police officer to accompany their every step.

But the birders contended that the advance notice was unworkable. Nobody could predict when a hurricane would hit, driving in many seabirds rarely seen in Virginia.

Lucius Kellam III, the bridge authority's interim executive director and son of the man for whom the bridge is named, was willing to find a compromise.

"Obviously, it can be done," he said. "The question is, at what cost and who pays?"

With Brinkley in the lead, the birders started researching.

Byrd called the Surrey nuclear power plant, which birders pass to get to a state refuge on Hog Island. Both coming and going, visitors to the refuge must stop so guards can check under their hoods.

Brinkley consulted with J. Christian Kessler, who heads the State Department's office dealing with export control and conventional arms nonproliferation. He also birds on the bridge.

"The fact is, certain security is necessary," said Kessler, who passes two checkpoints en route to his own office. "On the other hand, we can reach a point where the steps we're taking to protect our security start to so change the way we live that, in essence, we've permitted the terrorists to make us different than we want to be. And to give up some of what we valued and made us different and special."

After a month of imagining ways to thwart a terrorist, Brinkley recommended a middle ground replete with security measures, which he said was preferable to "handing victories to al Qaeda and other terrorist groups without a strong effort to maintain the lives we have lived and that we love."

He suggested that birders get access to the bridge islands by submitting to background checks with national law enforcement agencies, including the CIA and the FBI; agreeing to vehicle checks with undercarriage mirrors and searches by explosives-sniffing dogs and Geiger counters; and paying for identity cards that have magnetic strips. He further recommended the tunnels be equipped with detection devices for chemical and biological agents.

The birders pronounced themselves grateful for even the limited access.

Brinkley's only regret is that he could not convince anyone of the merits of training bird-watchers to be on the lookout for terrorists.

"I think there could have been a core of people who would be black belt bird-watchers," he said. "But no one wanted to coordinate it."

More than 350 species of birds have been spotted in the area of the Chesapeake Bay Bridge-Tunnel.