President George W. Bush is set to travel to Ukraine ahead of a high profile Nato summit in Bucharest next month, raising the stakes in a dispute within the alliance over how quickly the former Soviet state should proceed towards membership.

The US is pushing hard for Ukraine and Georgia to gain entry to Nato`s Membership Action Plan at the summit in three weeks time, according to western diplomats.

But they add that Germany, France, Greece, Italy, Norway and Spain are resisting the move, a significant milestone on the road to full membership, amid sharp differences over its implications for the alliance`s relations with Russia.

They fear the award of MAP status to the former Soviet states would worsen relations between Russia and the west, already hit by US plans to deploy a missile defence system in the Czech republic and Poland.

President Vladimir Putin, who will also be attending the Nato summit, has suggested that Moscow could target Ukraine with missiles should the country join the alliance or host US missile defence bases.

The US has appeared keen to avoid a public dispute with its Nato allies over the issue. "Although differences over Ukraine and Georgia surfaced at last week`s Nato meeting , there was general agreement to keep things quiet," said a western diplomat.

But yesterday, the White House was due to announce Mr Bush`s plans to visit Ukraine before the summit, as well as a subsequent trip to Croatia, which is expected to become a full Nato member at the gathering, together with Macedonia and Albania.

Nato enlargement to the east is seen as an important "legacy" issue for some Bush administration officials, who also insist the alliance must not be pushed off course by Russian intransigence.

"Whether on enlargement, missile defence, or a Membership Action Plan, Nato must make its own decisions for the right reasons," said Dan Fried, the State department`s top official responsible for Europe, this week, in reference to Mr Putin`s attendance at the summit.

However, Angela Merkel, German chancellor, this week signalled her concern about Nato`s enlargement, saying it should not involve countries "entangled in regional conflicts" - a clear reference to Georgia.

Berlin is starting to work on a compromise that would see Nato offering Ukraine and Georgia a newly created status below MAP, called the "Action Plan". However, one European diplomat questioned whether the concept had any real meaning.

Britain is positioned at the centre of debate, believing Ukraine and Georgia should get MAP status but that the Bucharest summit is not the right place to do it.

By James Blitz and Stefan Wagstyl in London and Daniel,Dombey in Washington,

The Financial Times