VIENNA, Austria — A senior U.S. envoy will sit eye-to-eye for the first time today with a top Iranian nuclear negotiator, a sharp reversal in U.S. policy that aims to entice Tehran into ending activities that could be used to make atomic weapons.

The move to send Undersecretary of State William Burns to the Geneva nuclear talks has raised the hackles of Washington hardliners who say it signals U.S. weakness. But supporters insist because both Tehran and the United States want to ease tensions, the move could breathe life into deadlocked nuclear talks.

On the eve of the meeting, French Foreign Minister Bernard Kouchner said the talks offered hope for a peaceful solution to the standoff over Tehran's nuclear program. But he also expects no quick changes from Iran, which has said "the essentials" — an apparent reference to suspending uranium enrichment — will not be on the table.

"After the Geneva meeting, we must not hope for an improvement, a change of attitude, right away," he said in Paris.

Setting the stage

Initially, supporters of the negotiations say, the U.S. and its allies could agree to stop pushing for new U.N. sanctions if Tehran stops expanding its uranium-enrichment capacities — setting the stage for fuller negotiations and what the West hopes will be agreement from Tehran to dismantle its enrichment program.

Uranium enrichment can produce both reactor fuel and the core of nuclear warheads. Iran says it has a right to enrich for peaceful uses and continues expanding its program despite three sets of U.N. Security Council sanctions sparked by concern that Iran's ultimate goal is to make weapons.

The Americans are part of a six-nation effort — the permanent Security Council members plus Germany — trying to encourage Iran to suspend its nuclear efforts in exchange for economic and political incentives.

The venue of today's talks reflects the potential significance of the meeting.

The Hotel de Ville, or city hall, stands at the top of Geneva's Old Town. Its neoclassical rooms have hosted important international negotiations since 1872, when an arbitration tribunal ordered Britain to pay the United States $15.5 million in Civil War damages. It was also the first home of the League of Nations, predecessor of today's United Nations.

The all-day talks, formally led by EU envoy Javier Solana and Iranian negotiator Saeed Jalili, start at 11 a.m.

American officials have insisted that Burns' presence will be a "one-time event" and he will listen to the Iranians but will not be negotiating. They also say the U.S. continues to demand that Iran fully freeze uranium enrichment — a point Secretary of State Condoleezza Rice again drove home Friday.

Sending Burns to Geneva is a "strong signal" that the United States is serious about diplomacy, but the U.S. continues to insist the start of negotiations with Iran is contingent on "the verifiable suspension of Iran's enrichment and reprocessing activities," she told reporters at the State Department.

Sending signal of weakness

Policy hawks disagree. John Bolton, former U.S. ambassador to the United Nations and undersecretary of state in charge of Tehran's nuclear file, said the move represents a "U-turn" in the U.S. stance on Iran.

"To the Iranians, it will send a sign of the political weakness of a (U.S.) administration in its last days and desperate for a deal," he said.

The United States and its five partners (Britain, France, Germany, Russia and China) have insisted all along that they want a full halt to Iranian enrichment. Still, Burns' decision to attend the Geneva talks shows that Washington may accept something less than full suspension, at least as a first step, to achieve its ultimate goal under a "freeze-for-freeze" proposal.

The "freeze-for-freeze" idea envisions a six-week commitment from both sides. Preliminary talks meant to lead to formal nuclear negotiations would start, Iran could continue enrichment but only at its present level, and the U.S. and its allies would stop pushing for new U.N. sanctions.

If that results in the start of formal talks, the Iranians would stop all enrichment temporarily. Those talks, in turn, are meant to secure Tehran's commitment for an indefinite ban on enrichment.

Iranian Foreign Minister Manouchehr Mottaki, speaking in Ankara on Friday, said the talks could also result in agreements to open a U.S. interest-protection bureau in Iran and establish direct flights between the two nations.

U.S. interests in Iran are now represented by the Swiss Embassy in Tehran.

Iran and the United States broke off diplomatic relations after the 1979 Islamic Revolution and hostage crisis at the U.S. Embassy in Tehran. Official contacts between the two countries are extremely rare.

If the Geneva talks make little progress, the White House will have some tough decisions to make, now that it has at least stretched — if not broken — its own rules on engaging the Iranians face to face on the nuclear issue.

The administration could decide to pull out of the six-nation group trying to entice Iran into negotiations.