The United States has stepped up pressure to prevent Europe from charging foreign airlines for greenhouse gas emissions when they take off and land there.

Yet even as authorities in the United States seek to build support against the European system, some major carriers in the United States have started taking steps to comply with the rules, which take effect in 2012. Participating now will enable airlines to avoid paying most of the cost of permits for their carbon emissions for years to come.

The law, which European Union governments approved two years ago, represents the boldest attempt by Europe to push other parts of the world to adopt its standards for controlling greenhouse gases. It has prompted bitter criticism from the airline industry in Europe and abroad, especially from carriers in the United States.

Under the law, airlines would not be charged for 85 percent of the cost of permits needed to cover their emissions until the end of the decade. Still, compliance would cost the industry at least 2.4 billion euros, or about $3 billion, a year, according to the International Air Transport Association, a trade group. It said much of the cost would be passed on to travelers in higher ticket prices.