The situation is reminiscent of the transatlantic crisis before the Iraq war when France and Germany refused to follow the US hard line. But this time Washington may not get its way.
"America believes the IAEA (International Atomic Energy Agency) must be true to its purpose and hold Iran to its obligations," Bush said in a speech in London on Wednesday.
The United States charges that Tehran is using what it says is a peaceful nuclear program as a cover for secretly developing atomic weapons.
Washington wants the IAEA to take tough diplomatic action against Iran but is strongly opposed by France and Germany as well as Britain, which was America's staunchest ally over Iraq.
The European position has majority support, including Russia, non-aligned and Latin American countries, on the 35-nation IAEA board of governors that is meeting Thursday at its Vienna headquarters, diplomats said.
Israeli Prime Minister Ariel Sharon on Wednesday called on EU president Italy to pressure Iran for guarantees about its nuclear programme.
Israel considers the Iranian nuclear program a serious threat to its existence.
Washington wants Iran to be declared in non-compliance of the nuclear Non-Proliferation Treaty (NPT), particularly for secretly making small amounts of plutonium and enriched uranium, while the European big three think this could lead Tehran to pull out of working with the IAEA.
A non-compliance ruling would bring the issue before the UN Security Council, which could then impose sanctions on Iran, a move Tehran has warned would cause an international crisis.
In a report last week, IAEA chief Mohamed ElBaradei detailed Iranian nuclear violations but said there was so far no evidence Iran was trying to make the bomb, a conclusion Washington dismissed as "simply too impossible to believe."
A draft resolution from the European big three prepared for the IAEA board meeting avoids citing Iran for non-compliance despite ElBaradei's reporting 18 years of hidden suspicious activities.
The British, French and German foreign ministers won key concessions of cooperation with the IAEA on a visit to Tehran on October 21, and want to avoid moves that might scale back further cooperation.
But US Secretary of State Colin Powell on Tuesday described as "just deficient" European readiness to treat Iran's change in attitude since October 21 as a new beginning.
Powell complained that the EU draft contained no "trigger mechanisms" setting performance benchmarks to determine whether Iran is to avoid diplomatic or other sanctions.
The EU's foreign policy chief Javier Solana stressed at a joint news conference with Powell in Brussels that the British, French and German foreign ministers had secured a pledge from Iran to agree to snap IAEA inspections and to suspend uranium enrichment.
The United States would like to see this suspension made permanent but Iran's top national security official said Wednesday that Iran would refuse this.
The gap between the US and European views is so great that "there is no certainty there will be a resolution," when the IAEA board meets, a diplomat in Vienna said.
Washington may be able to live with this, since there is another IAEA board meeting in March and more Iranian violations may be revealed before then, diplomats said.
But they said the EU was working on a revised text, possibly hardening the resolution by referring to "breaches" by Iran, after extensive lobbying from states like the Netherlands, New Zealand, Australia and Canada on behalf of the US position.