By Nick Childs BBC Pentagon correspondent

The United States has shaken off qualms about Nato enlargement and reform and is backing both at the alliance's summit in Prague. President George W Bush became a champion of "robust" Nato enlargement. And few in Washington questioned his position.

It was a far cry from the divisions in Washington a few years ago about whether enlargement was in itself a good idea.

Lord Robertson is an advocate of Nato reform

The arguments against it were that it would redivide and destabilise Europe and undercut the reformers in Russia.

There have been suggestions that some senior Pentagon officials were unhappy about whether some of the likely new members are really ready for Nato membership. But in the end the administration supported the full list of seven countries.

A 'relevant' Nato

There are several reasons for the change of heart in Washington.

One is the way the first round of post-Cold War enlargement developed.

Poland, the Czech Republic and Hungary have proved enthusiastic Nato members and have seemed particularly anxious to please the United States.

Washington is also much more positive about the role of an enlarged Nato in creating a Europe that is "whole, free and at peace", as the mantra goes.

Russia's relationship with Nato has improved since 11 September

But perhaps the most significant change concerns the impact on relations with Moscow.

Russia has essentially embraced the notion of enlargement, as it has itself been embraced in a new and closer relationship with the Alliance.

It is a phenomenon that has been accelerated under President Vladimir Putin in the aftermath of the attacks against the United States on 11 September 2001.

But the Prague summit is being dubbed a "transformation" rather than an "enlargement" summit.

Driven by the United States, Nato is looking to reform itself to deal with new threats, like terrorism and weapons of mass destruction.

The quest is to keep Nato "relevant".

This could in the end prove more significant than the acceptance of seven new former Soviet bloc members.

Increasing capabilities

The changes are likely to include a more streamlined command structure and the endorsement of a US idea for a rapid response force that could deploy quickly beyond Europe's borders.

The US wants Nato to be able to deal with new types of threat

The Pentagon would like to see its European partners focus on boosting key areas, like secure communications, defences against weapons of mass destruction and deployment capability.

One initiative the Pentagon would like to see emerge develop is for its European allies to work together to lease expensive cargo and tanker aircraft to give their forces greater range and flexibility.

The Nato Secretary-General, Lord Robertson, is an enthusiastic advocate of these changes.

Most Nato allies also acknowledge the need for reform. Whether they all want to go as far or as fast as Washington is another matter.

Iraq test

As for Iraq, that is bound to be discussed.

The US National Security Adviser, Condoleezza Rice, has said she expects a statement on Iraq from Nato.

The unfolding of the Iraq crisis has worked out quite conveniently for the alliance.

Unless there is a serious showdown in Baghdad this week, Nato members can unite around the new UN Security Council resolution without having to take any decisions on military action.

But Dr Rice said she expects that the Americans will hear from their Nato partners what they are willing and able to do about Iraq.