The 19-member former Cold War military bloc, which had been expected to admit seven new members at a June summit in Istanbul, is now planning on an enlargement ceremony in the next few months, sources say.

The push for help in policing eastern Europe's skies comes in particular from the three ex-Soviet Baltic republics Estonia, Latvia and Lithuania, as well as Slovenia.

"The incoming member countries have virtually no air defences, and they are keen to come under the NATO system," said an alliance official, speaking on condition of anonymity.

Officials at NATO's Brussels headquarters are in "intense discussions" on the issue with the new members -- also including Slovakia, Romania and Bulgaria -- who may now join at a ceremony during the spring.

Moves to bring forward the formal accession date were decided on after the Istanbul summit date was put back by about a month. In addition the ratification process in member states has gone quicker than expected.

The seven newcomers were invited to join NATO at a summit in Prague in November 2002, following three other ex-communist states -- Poland, Hungary and the Czech Republic -- which joined in 1999.

"Certainly, all countries concerned would like to have NATO air policing cover in place by the time of accession," said a Lithuanian diplomat, adding: "Given the current state of discussions within the alliance, we hope for very rapid progress over the coming weeks and months."

"It is urgent that we find a solution so that these countries get this air cover which is fundamental," added the NATO official.

Apart from some 20 AWACS air surveillance aircraft, NATO itself does not possess any military hardware, relying on member states to provide resources -- in this case fighter jets able to patrol skies over the alliance newcomers.

The need was amply demonstrated during the 2002 Prague summit, when the Czech Republic had to call on US aircraft to protect the airspace over the summit venue.

The problem is that, with NATO member states already stretched with commitments in hotspots from the Balkans to Iraq and Afghanistan, it is proving difficult to find air power to protect the relatively unthreatened newcomers.

In a recent interview with the French daily Le Figaro, NATO's chief commander in Europe, US General James Jones, said the question of air defences for the Baltic countries should be on the agenda for the June summit.

Lithuania for example has an airforce of barely 800 people, and depends heavily on its fellow Baltic states. All three states rely for the most part on surface-to-air missiles.

Vilnius has no fighter jets, and was "strongly advised" by NATO "not to invest into combat aircraft," said the Lithuanian diplomat.

But this leaves it in a situation where, if the alliance cannot provide air protection, it will be forced to strike bilateral deals, or drop investments asked of it to meet NATO standards.

"The number of aircraft that is necessary is small... we do not expect to get this coverage for nothing and are ready to discuss all the conditions and modalities of this cooperation," said the Lithuanian diplomat.

"Political will would help us move forward on this issue," he added.

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