Washington has dropped its objections to Mohamed ElBaradei serving a third term as the head of the UN nuclear watchdog - the International Atomic Energy Agency (IAEA).
By Jonathan Beale
BBC News, Washington
The apparent change of heart follows a meeting between Mr ElBaradei and Condoleezza Rice on Thursday.
ElBaradei has not said Iran is working on nuclear weapons
After their meeting, the state department said the US would join the consensus - conceding that if there was a vote today, that would mean supporting Mr ElBaradei to serve a third term.
State department spokesman Sean McCormack said: "We are going to join the consensus. And I think that, based on the news reports that I see out there today, the vote would have Dr ElBaradei continuing at the IAEA. And we would join such a consensus."
Officially, the US always made out that its objection was a matter of protocol, rather than personality.
Even now, the US says it believes in the principle of the head of the IAEA serving just two terms.
But behind the scenes there was also strong opposition to the man himself.
Some senior officials viewed Mr ElBaradei as an obstacle in their efforts to confront countries trying to obtain nuclear weapons.
Some officials viewed him as unhelpful in the run-up to the Iraq war.
John Bolton was seen as a leading light of the "get ElBaradei out" campaign.
As America's chief negotiator on arms control, he favoured confrontation. But Mr Bolton's influence may have waned as he found himself and his style under the spotlight.
Mr Bolton is President Bush's nomination as the next US ambassador to the United Nations, but he is still to be approved by the US Senate.
Now attention has turned to Iran. Israel estimates that Iran could have a nuclear weapon within two years.
Mr ElBaradei has so far not backed the US position that Iran is trying to build nuclear weapons under cover of a civilian programme.
Europeans believe his caution may give him more credibility. The IAEA is certainly investigating Iran's intent.
Mr ElBaradei is pressing Tehran for answers about its nuclear programme which it hid from the agency for more than a decade.
The IAEA is trying to verify whether Iran has suspended its uranium enrichment programme.
There is no doubt the US wants a strong referee in judging whether Iran is complying.
America is supporting efforts by the European Union to persuade Iran not to resume its uranium enrichment programme.
Last month, the EU-Three (France Germany and Britain) managed to avoid a crisis when Iran agreed to shelve its plans to resume enrichment - in return for trade incentives.
Polls in Iran will have an impact on uranium enrichment plans
But Iran has also made clear that the cessation is only temporary.
The big worry for the US administration is what happens if the EU negotiations eventually fail.
They will need strong support to refer Iran to the UN Security Council. And Mr ElBaradei could play a critical role.
All eyes are now on Iran's presidential elections scheduled for 17 June.
The former president - Akbar Hashemi Rafsanjani - is the frontrunner.
His hope is that he will work with the US and EU to cease uranium enrichment.
But he is also the father of Iran's nuclear programme and has made clear that he believes Iran has a right to enrich uranium for a civilian programme.
In return for supporting Mr ElBaradei, the US will expect him to take a tough line on Iran. But the IAEA insists that there were no conditions attached to US support.