The Bush administration, on the eve of a critical meeting in Vienna, has offered to join nuclear talks with Iran if Tehran stops enriching uranium. President Bush said the move shows the United States is taking a leadership position in trying to resolve the Iranian nuclear issue diplomatically.

The Bush administration had previously let European allies Britain, France and Germany take the lead in the nuclear dialogue with Iran.

But in a major policy shift, the United States is now willing to take a direct role in the talks if Iran verifiably suspends uranium enrichment and reprocessing.

The announcement came on the eve of a meeting in Vienna Thursday of foreign ministers of the five permanent U.N. Security Council member countries and Germany, who are seeking final agreement on a package of incentives to get Iran to halt sensitive nuclear activities and return to negotiations.

The so-called carrots-and-sticks approach by the major powers would also include punitive steps starting with a Security Council resolution against Iran if it spurns the incentives.

The United States has been pressed by other participants in the diplomatic process to become directly involved, and Wednesday's decision could help expedite an agreement in Vienna.

Paul Kagame (l) with President  Bush in the White House

President Bush, in a press appearance with Rwandan President Paul Kagame, said the move underlines the administration's determination to resolve the Iran nuclear issue by political means.

"I believe it is very important that we solve this issue diplomatically, and my decision today says the United States is going to take a leadership position in solving this issue," said President Bush. "And our message to the Iranians is that, one, you won't have a weapon, and two, that you must verifiably suspend any programs, at which point we will come to the negotiating table and work on a way forward."

The United States has had no diplomatic relations and few official contacts with Iran since 1979.

Secretary of State Condoleezza Rice gestures during a news conference discussing the nuclear standoff with Iran, Wednesday, May 31, 2006

At a news conference, Secretary of State Condoleezza Rice made clear the U.S. administration is not ready to talk about resuming diplomatic ties given what she said were the many fundamental differences it has with the Iranian government.

She also said the policy change should not been seen as conferring legitimacy on what she said is an Iranian regime that denies its people political rights and supports terrorism around the world.

"The only thing that is being provided legitimacy here is the international community's consensus that Iran must suspend its current enrichment and reprocessing activity, return to serious negotiations, find a civil nuclear program that does not have proliferation risks associated with the fuel cycle, and negotiate in good faith," said Condoleezza Rice. "That's what's being provided legitimacy."

Under questioning, the Secretary again said the United States does not rule out a military option in dealing with what U.S. officials believe is a covert Iranian nuclear weapons program, but said it is committed to diplomacy and that many diplomatic options remain.

The U.S. policy move was welcomed by European allies and International Atomic Energy Agency chief Mohamed elBaradei, among others.

The Iranian government had no immediate comment on the offer though one Tehran spokesman was quoted as saying the U.S. condition for dialogue was not suitable.

Iran, which contends its nuclear program is entirely peaceful, has said it has a right to a complete nuclear fuel cycle and will not return to a complete suspension of enrichment activity.