European officials are increasingly concerned that Sen. Barack Obama's campaign pledge to begin direct talks with Iran on its nuclear program without preconditions could potentially rupture U.S. relations with key European allies early in a potential Obama administration.

The U.N. Security Council has passed four resolutions demanding that Iran stop enriching uranium, each time highlighting the offer of financial and diplomatic incentives from a European-led coalition if Tehran suspends enrichment, a route to producing fuel for nuclear weapons. But Obama, the presumptive Democratic presidential nominee, has said he would make such suspension a topic for discussion with Iran, rather than a precondition for any negotiations to take place.

European officials, speaking on the condition of anonymity, said they are wary of giving up a demand that has been so enshrined in U.N. resolutions, particularly without any corresponding concessions by Iran. Although European officials are eager to welcome a U.S. president promising renewed diplomacy and multilateralism after years of tensions with the Bush administration, they feel strongly about continuing on the current path.

"Dropping a unanimous Security Council condition would simply be interpreted by Iran and America's allies as unconditional surrender, and America's friends would view this as confirmation of America's basic unreliability," said Francois Heisbourg, a Paris-based military analyst with the International Institute for Strategic Studies. "A hell of a way to start a presidential term."

The United States does not have formal diplomatic relations with Tehran, unlike the other countries in the coalition. Obama advisers contend that U.S. willingness to engage directly with Iran would improve a process that they say is not effective in thwarting Iranian ambitions. "People say we can't give something for nothing," said Susan Rice, a key Obama foreign policy aide. "But every day that passes, the Iranians are getting something for nothing — progress on their nuclear program."

Obama advisers appear to distinguish between full negotiations and preparatory talks with Iran, stressing that the most immediate consequence of their approach is that a U.S. official likely would accompany European Union foreign policy chief Javier Solana when he meets with Iranian representatives, a shift European officials said they would welcome.

Still, Philip H. Gordon, a Europe expert at the Brookings Institution who has advised the Obama campaign, acknowledged that European officials "are uncomfortable with giving up the precondition of uranium enrichment right now." Gordon, who emphasized he was not speaking for the campaign, said the dynamic has changed in recent years, so that "after all the lies and dissembling by the Iranians, the European negotiators have become pretty hard-line" on Iran.

European officials, who spoke on the condition of anonymity because they did not want to be seen as interfering with U.S. politics, said the demand that Iran first suspend its uranium enrichment is a European concept, not something forced on them by the Bush administration. Three European countries — Britain, France and Germany — persuaded Tehran to suspend its enrichment activities in 2003 while the two sides negotiated, until Iran declared in 2006 that the talks were fruitless and restarted their nuclear program.

After the United States, Russia and China joined the European-led effort in 2006, the six nations jointly offered a large package of incentives if Iran would once again suspend enrichment. This month, the six sweetened the terms of the deal — and European leaders warned that Iran faces even tougher sanctions if it does not stop its nuclear work. But Iran has shrugged off the offers and threats and is building a stockpile now estimated at 150 kilograms (330 pounds) of low-enriched uranium.

European officials say they are not prepared to start negotiations on the package of incentives while Iran continues its enrichment activities. "Formal negotiations can start as soon as Iran's enrichment-related and reprocessing activities are suspended," declared a June 12 letter to Iran's foreign minister, signed by all six foreign ministers in the coalition, including Secretary of State Condoleezza Rice.

President Bush, during his farewell tour of Europe last week, pointed to the coalition as one of his foreign policy legacies. "I leave behind a multilateral framework to work this issue," Bush said. "You know, one country can't solve all problems. I fully agree with that. A group of countries can send a clear message to the Iranians."

But in a recent interview on CNN, Susan Rice, Obama's adviser, was blunt in her criticism of the current approach. "Before we will talk to them about their nuclear problem, they have to suspend their nuclear problem. That (is a) counterproductive precondition," she said.

Obama, during a speech this month to the American Israel Public Affairs Committee, argued that Iran's growing expertise in uranium enrichment meant there is "no time to waste" and that it is "time for the United States to lead." He dismissed the Bush administration approach as "limited, piecemeal talks while we outsource the sustained work to our European allies." But, he added: "There will be careful preparation. We will open up lines of communication, build an agenda, coordinate closely with our allies and evaluate the potential for progress."

Obama's Republican rival, Sen. John McCain, Ariz., has lauded the European efforts, saying in April that the coalition "deserves praise for its great efforts to present a positive endgame: an Iran with far-reaching economic incentives, external support for a civilian nuclear energy program and integration into the international community."

"Obama criticizes a multilateral process and disparages the European contribution. What he is proposing is unilateral cowboy summitry," said Randy Scheunemann, the McCain campaign's national security director. He said McCain "agrees we need to have basic benchmarks, such as suspension, before you go further. And he has called for a significant increase in sanctions, through the U.N. if possible or through like-minded allies if necessary."

Obama campaign officials, however, dismiss the current effort as "weak carrots and weak sticks" and argue that U.S. willingness to engage Iran could be used to prod both Iran and U.S. allies — such as by seeking an upfront commitment from Europe, Russia and China to support much tougher sanctions if the negotiations fail.

"This will give us stronger carrots and stronger sticks," said Dennis Ross, a Middle East envoy in the Clinton administration who advises the campaign and acknowledged he has heard concerns from Europeans. "This will give us leverage with those who are convinced Iran should be stopped but have not provided tough economic sanctions," such as ending financing of Iran's energy businesses. "This will not take place divorced from the U.N. Security Council. But we have to be mindful we have a process that is not working."