Airlines and their passengers are beset by soaring costs for fuel, insurance and security. Now they may also face bills for polluting.

Next month, the European Union aims to present its strategy for making airlines pay a levy for the carbon dioxide their planes emit. The plan, if approved, could hit consumers in the wallet by adding as much as $100 to the price of an airline ticket from Europe to the United States, by some calculations, and smaller amounts to flights within Europe.

More troubling for the strapped airline industry, the European Union could spark a global fight if it follows through on a proposal to include non-E.U. airlines in its plan because the U.S. government and the United Nations' aviation regulator say the European Union has authority to force only airlines from the 25-country bloc to pay for emissions. The issue is shaping up as one of the next big battles in the aviation industry.

Carriers say politicians risk crimping people's ability to afford flying by imposing big bills for polluting. Environmental activists counter that ballooning air travel is itself the problem, because aircraft, operating at high altitude, may have a disproportionately strong impact on the global climate.

Some environmental groups even say air travel is too inexpensive -- and they advocate cutting traffic through hefty taxes.

The issue has gained prominence since the Kyoto protocol on global warming came into force in February. Aviation isn't covered by the treaty, but environmental activists say airlines shouldn't get special treatment.

The European Union wants to make airlines pay to reduce or offset the carbon dioxide that aircraft produce from burning jet fuel as soon as 2008. "Our goal is for airlines to take responsibility for their CO2 emissions," said Barbara Helfferich, spokeswoman for E.U. Environment Commissioner Stavros Dimas.

E.U. officials favor adding airlines to the emissions-trading program the European Union started on Jan. 1 to meet its Kyoto obligations. Under the system, polluters in a number of industries -- including oil refining, power generation and steelmaking -- are granted the right to emit a set amount of carbon dioxide. Beyond that, they must buy emissions credits that trade on an open market and are partially linked to projects that reduce carbon dioxide emissions around the world. The levy isn't a tax because the money wouldn't go to general tax coffers. The European Union is also considering options for airlines, including taxes or other types of charges.

Whatever shape the emissions levies take, airline tickets are likely to be one of the first places consumers feel the cost of environmental policies in Europe, the region that is acting most forcefully to tackle global warming. The pinch will be especially evident if airlines itemize the emissions costs on their tickets, as they already do with some taxes and fees.

Consumer reaction could shape future policies on emissions payments for cars and other nonindustrial pollution around the world.

The cost could be huge to the global airline industry, which officials predict will lose about $9 billion this year because of fuel prices. A study by the U.N. International Civil Aviation Organization estimates that a system to charge carriers worldwide for the greenhouse gases they produce could cost $17 billion to $60 billion annually, depending how tight the standards are.

A Swiss environmental group, MyClimate, estimates that each passenger's slice of an airline's bill for emissions credits would boost the price of a round-trip ticket between London and Paris by about $20, and between London and Los Angeles by almost $100.

The United States, which has not signed the Kyoto protocol, has opposed pollution charges for airlines. At an ICAO meeting last year, the United States succeeded in postponing discussion of global measures until at least 2007.

One E.U. proposal is to treat all carriers equally by imposing a charge on each flight lifting off in an E.U. country. An ICAO spokesman in Montreal said the move would be illegal, but E.U. officials say its even-handedness would make it legal.

U.S. industry officials say they would fight E.U. pollution levies and instead look to ICAO, which establishes global standards for aviation.

"The ICAO work is critical, because that's where worldwide policy is set," said Nancy Young, an attorney at the Air Transport Association, a trade group in Washington.