The United States must take another step towards a global climate change pact when major industrialized countries meet in Japan next week, the head of the European Union's executive said on Friday.

"In this G8 summit we will expect the United States to show more ambition than they have shown so far," European Commission President Jose Manuel Barroso told reporters.

He noted a recent narrowing of differences between Brussels and Washington on the need to tackle emissions of greenhouse gases linked to rising global temperatures, but the two sides remained far apart on how to do it.

EU officials said that, without a step forward by U.S. President George W. Bush, there was little chance of progress until late next year when countries would be rushing to try to thrash out a new U.N. climate change deal.

The next round of U.N. climate talks is due to take place in Poland in December, but the United States will be in transition, before the inauguration of its next president in January.

"The world expects more from a major economy like the United States," Barroso said. "I am saying that not just as a hope -- I expect the U.S. will accept a more ambitious conclusion at the G8 than the one last year."

At a Group of Eight summit last year, leaders of the world's richest countries agreed to consider seriously a global goal of halving greenhouse gas emissions by 2050.

Now the EU wants the G8 to fix that goal and agree on the need for a target for cutting emissions by 2020, although officials in Brussels concede there is little chance of the Bush administration backing the idea of a near-term goal.

Barroso said a 2050 target would not be credible without a closer goal, too. He said he expected the next U.S. president to "enhance" the shift in Washington's position towards measures already agreed by the EU.

The 27-nation EU has agreed to cut its greenhouse gas emissions by at least 20 percent from 1990 levels by 2020 and is now working on rules on emissions by industry, cars and aircraft and other legislation to meet that target.

The United States says it is committed to fighting climate change but refuses to accept binding emissions cuts until big developing economies such as China and India agree to mandatory limits.