A dispute over whether U.S. airlines will have to offset the carbon they emit on flights to and from Europe may be inching closer to a diplomatic breakthrough, according to officials involved in the negotiations.

In January, the European Union began implementing an Emissions Trading Scheme, which compels airlines to buy carbon allowances for flights landing in and taking off from Europe. The U.S. government — along with the governments of 79 other countries — objects to the program.

The European Commission estimates the program could add between $2.66 and $15.96 to the cost of a ticket over the coming decade; airlines will start paying the fee in April 2013.

On Tuesday, Airlines for America, the trade group that unsuccessfully sought to block the program through European courts, dropped its legal appeal and said it hoped the Obama administration would continue to fight the policy through diplomatic measures.

Nancy Young, the trade group’s vice president for environmental affairs, said that if the E.U. did not respond to the administration’s objections, “We would assume that the U.S. would ratchet [the political pressure] up again.”

But European Commissioner for Climate Action Connie Hedegaard, who met with U.S. Transportation Secretary Ray LaHood on Wednesday, said she is optimistic that her government can forge a compromise with other countries on a global allowance trading system through the U.N. International Civil Aviation Organization (ICAO).

“There is a will to try to look for a solution,” she said in an interview, adding she was encouraged that the U.N. group decided two weeks ago to analyze four different options for trading carbon allowances. “What matters is the end result is good for the climate.”

Both the Obama administration and a bipartisan group of lawmakers — including House Transportation and Infrastructure Committee Chairman John Mica (R-Fla.) and ranking member Nick J. Rahall (D-W.Va.) — reiterated Wednesday that they would only accept a global trading system brokered by the U.N.

“Addressing aviation emissions is a laudable goal, but it is a global issue that will only be addressed with a global solution,” Rahall said in a statement after the committee held a public roundtable discussion with administration officials on the matter Wednesday. “The EU’s go-it-alone approach not only flies in the face of international law, but it is also jeopardizing the ability of the international partners to reach global consensus on how to move forward.”

In an interview, the State Department’s deputy assistant secretary for transportation affairs, Krishna R. Urs, said, “The E.U. has to find a way to make it clear they’re open to a resolution in ICAO that’s achievable and that takes into account all of the interests of everybody else.”

“Being put under the gun by the E.U. has gotten everyone’s attention,” said Sarah Burt, a staff attorney at the advocacy group Earthjustice. But she added she was worried any internationally-brokered compromise would not deliver steep enough cuts in greenhouse gas emissions linked to global warming. “I’m less optimistic that the system will be stringent enough to make a real difference.”