Over the past three decades, with airplanes hijacked to Cuba, intentionally blown up over Scotland, and exploding mysteriously off Long Island, federal and local officials have repeatedly examined the effectiveness of airport security in the United States.

Yet through all the incidents, and the many government studies they provoked, the structure of airline security changed little: private airlines and airport operators were held responsible for keeping aircraft and airports safe, usually without much financial help from the government. What has resulted is a tangled system in which the industry tries to keep down the costs of complying with federal rules on aviation security, and government regulators, sympathetic to the industry's problems, do not always insist on levels of security that have been adopted in some foreign countries.

Now, as the images of hijacked airplanes plowing into the World Trade Center and the Pentagon are still fresh, there is a fundamental rethinking underway. Airport officials, lawmakers and safety experts say airport security should be drastically overhauled, and perhaps billions of dollars invested in high-tech surveillance and other anti-terrorist tools, including simple things like better pay for airport workers.

Some are also suggesting that airport security has become an issue of national security and should be made a function of the federal government. Even the profit motive of local airport operators has come under question, as some critics have said the drive to make money from concessions like clothing stores and restaurants has helped make airports more vulnerable to terrorists.

''We have to create a federal agency security force, with high morale, high training, constant hiring and good benefits,'' said Neil C. Livingstone, chairman and chief executive of GlobalOptions, an international risk management firm. ''We don't ask any other industry in the United States to take over a life and death security function. For airlines, maintenance has always been the major issue, and that is what you want the airlines to concentrate on.''

Judging from some of the ideas being discussed, the airport of the future could include large security cones, which would be enclosed structures where passengers would be screened by machines that read molecular structures of the items they wear and carry. There could also be facial recognition technology, which would compare physical characteristics of passengers to those of known and suspected terrorists.

Vast networks of surveillance cameras could be set up, backed up by undercover security personnel posing as passengers and airport workers. Restaurants and shops could be banned or placed in airport areas distant enough to be regarded as low risk. Giant walls with razor wire and floodlights could replace chain-link fences on the airports' perimeter.

And following the example of places like Ben-Gurion Airport near Tel Aviv, passengers might be subjected to intense pre-boarding interviews conducted by highly trained screeners. Personal questions would be the norm, and a refusal to answer would mean missing the flight.

''Money is not an issue here in the first term,'' said Raymond W. Kelly, the former commissioner of the United States Customs Service who was named Sunday to a new federal commission looking at ways to improve airport security. ''Money clearly was an issue with turning the airport security over to the airlines in the first place. It doesn't take a genius to figure out they are a profit-making organization, and they are going to cut costs in any way they can.''

But even as the drive to make airports safer gathers force, security experts say there is no such thing as a fortress airport, especially in a large democracy that also places a premium on rights like privacy and individual liberty.

Unless terrorists are kept out of the country, or are identified through intelligence once they enter, the most expensive and sophisticated screening techniques will ultimately fall short, the experts said.

''The United States government could use the entire federal budget for aviation security, and there will still be vulnerabilities that can be exploited by a sophisticated terrorist,'' said Richard W. Bloom, director of terrorism, intelligence and security studies at Embry-Riddle Aeronautical University, based in Daytona Beach, Fla. ''Intelligence is really the name of the game here.''

Right now, the security of airports and airliners is managed under a convoluted system where airport owners, airlines and the Federal Aviation Administration all have overlapping responsibilities.

The system was first put into place by order of the government in 1973, after a nasty spate of airline hijackings.

The decision then was to place responsibility for screening passengers on the airlines themselves, although the security measures would be subject to government oversight.

The thinking then was that the airlines would have the greatest incentive to make sure the system worked smoothly and efficiently because they would pay the price for any failings. It is the same thinking that gives airlines responsibility for aircraft maintenance.

What's more, ''it was a fairly simple thing back then,'' said Bonnie Wilson of the Airports Council International, a trade group. ''You just had to keep guns off the planes.''