US President George W. Bush will host a ceremony on Monday with the prime ministers of Estonia, Latvia, Lithuania, Slovakia, Slovenia, Bulgaria and Romania to seal their entry into the currently 19-member US-dominated alliance.

The White House event, when the newcomers will deposit their accession documents to NATO's founding Washington Treaty and so become members, will be followed by a formal flag-raising ceremony at the alliance's Brussels headquarters April 2.

"This will be a huge step towards a long-standing objective of the alliance: a Europe without dividing lines. A Europe not only free of war, but also free from fear," said NATO chief Jaap de Hoop Scheffer, who will attend the event in Washington.

National celebrations are also planned in the new member states for the expansion, which comes less than two years after their formal invitation to join at a November 2002 NATO summit in Prague.

Three other ex-communist countries -- Poland, Hungary and the Czech Republic -- joined the West's former Cold War military bloc in 1999.

The United States has done little to disguise its satisfaction that the new NATO members were staunch supporters of its actions after the September 2001 attacks in the United States, notably in last year's Iraq war.

The seven "have already acted as allies through their strong solidarity and actions in the war on terrorism, and in helping to strengthen peace and democracy in Afghanistan and Iraq," a White House spokesman said Tuesday.

The Brussels ceremony will be attended by the newcomers' foreign ministers, who will then join an informal meeting with their counterparts from the newly-expanded 26-member organization.

The process of ratifying the newcomers' accession - which involves an amendment of the 1949 treaty which launched NATO after World War II -- has proceeded remarkably quickly, diplomats say.

Five of the seven new NATO states are also gearing up to join the European Union on May 1, finally cementing their re-integration into the transatlantic community after the end of the Cold War a decade and a half ago.

But amid the celebrations at least one cloud remains: Russia's continuing resistance. Moscow long opposed expansion, but was persuaded reluctantly to accept it two years ago, a process eased by geopolitical shifts following the September 11 attacks.

Specifically, Russia is opposing NATO plans to station warplanes and air defences in the ex-Soviet Baltic republics of Estonia, Lithuania and Latvia, plus Slovenia, which have no such defences of their own.

"It is clear that such plans directly threaten Russia's security," Russian foreign ministry spokesman Alexander Yakovenko said recently, warning that Moscow could take "corresponding measures" if necessary.

From a military standpoint, the seven newcomers' contributions will be relatively modest. They will be pressed to work hard to bring themselves up to NATO standards to ensure inter-operability in the expanded alliance.

But the enlargement will radically reshape Europe's security map: apart from neutral countries like Ireland and Austria, the only states outside NATO will be the ex-Yugoslav states, plus countries like Albania and Ukraine.

NATO officials stress that this will change, in time. Pressure is growing for a summit in Istanbul in June to extend invitations to Macedonia, Croatia and Albania to join, perhaps in 2006.

Bosnia-Hercegovina and Serbia-Montenegro are currently pushing to join NATO's Partnership for Peace program of enhanced cooperation, but it remains unclear when decisions on these cases could be taken.

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