AUGUSTA – After the Sept. 11 terrorist attacks, Bob McGee lost the parking lot of the airport he manages.

Then he lost the passengers and the revenues they generate. Now he worries the Augusta State Airport might lose its scheduled commercial flights as well.

The crushing cost of increased security is taking its toll at Maine’s four midsize airports. Those airports have financial difficulties in the best of times, but now are simply trying to survive.

“It’s been a confusing time,” McGee said. “We get two or three [safety advisories] a week, and sometimes they are conflicting. We are still at a heightened state of security and, one day, we may have to say that we are no longer in the scheduled airline business.”

Scheduled air service to airports in Augusta, Bar Harbor, Presque Isle and Owls Head is vital for the economies of those regions. Losing those services could make it harder for companies to move personnel around the world and to court new industries.

They all must maintain the same screening and security measures, no matter how small they are. There is no room for substantial drops in revenue because some people are afraid to fly.

In the days after the terrorist attacks, attention focused on the state’s large airports in Bangor and Portland. They have been promised federal help to cover extra security expenses, and also have the passenger volume and reserve accounts to pay for additional security spending.

Small general aviation airports such as Lewiston-Auburn and Sanford also confronted relatively minor problems after the Sept. 11 attacks.

Those facilities, which rent space to flying clubs, private plane owners and small charter operations, now remind users to be more watchful. Wiscasset Municipal Airport closed down temporarily last week because of its proximity to the Maine Yankee nuclear power plant.

But Maine’s midsize airports appear to face the greatest challenge due to the fallout of Sept. 11. These four airports have regularly scheduled flights to Boston provided by Colgan Air, a division of US Airways.

“These municipalities enjoy the economic benefits of commercial service,” said Philip W. Simpson, an airport management consultant based in Wiscasset. “But these airports don’t make enough money to make ends meet as it is. The question is how long the municipalities or counties are willing to support them.”

In Augusta, McGee said increased security meant he went from about 300 parking spaces to 18 when federal authorities required him to move all cars beyond a 300-foot perimeter.

Without parking, the airport loses income, and passengers can’t leave cars at the airport or return rental cars. McGee said he had to limit the airport’s car rental agency to three cars on site at a time.

The federal government also required that police officers watch the passenger screening process. That meant paying for an officer to be on hand 14 hours a day, working overtime shifts.

“That is expensive,” McGee said.

Meanwhile, the passenger count has fallen from 800 to 400 a month. That, McGee said, has further reduced airport revenues because there are fewer people paying the mandatory airport fee.