Efforts by ex-Soviet Ukraine and Georgia to start early talks on NATO membership took a knock on Thursday as allies disagreed on whether to embark on moves that would risk antagonising Russia.

Separately, NATO foreign ministers agreed in principle to invite Croatia and Albania to join the bloc at an alliance summit in April, but a cloud remained over Macedonia's bid as Greece threatened to block it in a row over its name.

Diplomats said Germany and France led resistance by half a dozen western European nations to a push by eastern ex-communist countries to offer Ukraine and Georgia a "membership action plan" (MAP) at an April 2-4 summit in Bucharest.

"We are continuing our consultations. The decision will not be taken until Bucharest," U.S. Secretary of State Condoleezza Rice told a news conference.

Membership for Ukraine and Georgia is still several years away. Even backers such as Washington are wavering on whether to offer MAP status in April in Bucharest - which outgoing Russian President Vladimir Putin plans to attend - or wait until later, perhaps at a summit to be held next year.

Both aspirant countries have recently suffered bouts of political instability. Polls show strong public opposition to NATO membership in Ukraine, while Georgia's democratic credentials were called into question last year by a state of emergency it imposed to choke off opposition protests.

German Foreign Minister Frank-Walter Steinmeier told reporters before the talks that Berlin was sceptical of their bids, while Luxembourg's Jean Asselborn noted NATO decisions had a bearing on neighbours such as Russia.

"We think that EU-Russia relations are absolutely important," said French Foreign Minister Bernard Kouchner, noting his country takes over the rotating presidency of the EU in July and wanted to talk with Russia about energy ties.

FROSTY

Russia cannot block NATO membership steps but allies know that deepening ties with Ukraine and Georgia would strain relations with Moscow, which are already frosty over Kosovo's independence from Serbia last month and the possible deployment of a U.S. missile shield.

Aspiring NATO states can only enhance their ties with the alliance if all 26 members agree, meaning Kiev and Tbilisi have an uphill task to persuade the doubters in coming weeks.

"Nobody questions their right for membership. There are doubts about the level of preparedness," said Polish Foreign Minister Radek Sikorski, whose country alongside Baltic states has been a strong backer of Ukrainian and Georgian hopes.

Foreign ministers broadly backed the aspirations of a trio of Western Balkan countries - Croatia, Albania and Macedonia - to receive invitations to join at the Bucharest summit.

But Greece reaffirmed it could not support Macedonia's entry into NATO for now, accusing Skopje of nationalist intransigence in a dispute over the former Yugoslav republic's name.

Greece rejects the name Macedonia because it says it implies territorial ambitions towards Greece's own northern province of Macedonia, birthplace of Alexander the Great.

Greek Foreign Minister Dora Bakoyanni said she told fellow ministers Macedonia's attitude could leave Athens no alternative but to use its veto.

"As far as the Former Yugoslav Republic of Macedonia is concerned, I stressed that the policy of our neighbour country does not allow us to take the same positive view as regarding Albania and Croatia," Bakoyanni told a news conference.

Diplomats said there was a general consensus that NATO should go ahead and issue invitations to Croatia and Albania even if Macedonia's request was blocked.