The decision by the US to send an official to meet Iran directly this weekend is a useful shift in its tactics – one that it should have taken a long time ago.

The debut performance of William Burns, the third-ranking diplomat in the State Department, in Geneva this weekend will not make much difference to the substance of the talks. The US has always made its presence known in the six years of attempts, led by Britain, France and Germany, to persuade Iran to scale back its nuclear ambitions. It just hasn’t been there in person. Three years ago, as European diplomats gathered in Geneva for another encounter with the Iranians, one Western official watching Jack Straw, then the Foreign Secretary, talking intently on his mobile phone while walking on the smooth lawns high above the lake, said laconically: “There he is again, getting his orders from Condi.”

That is a gibe that Straw always rejected. But the US, while sceptical of the European conviction that it was worth talking to Iran, helped to shape the talks. It pushed the EU to insist that Iran suspend uranium enrichment, the most controversial work, before it was rewarded; and it has been the architect of banking sanctions. It has also spun out the ambiguity over whether it or Israel would launch military action.

In sending Burns (although just to Geneva, not Tehran) the US has made a small shift – as it has in its recent exploration of whether to staff the US section of the Swiss Embassy in Tehran. The reckoning was that lines of Iranians queueing to get US visas would be a powerful advertisement, as well as playing to the pro-US sentiment of ordinary Iranians. Iranian officials appear to have agreed, in blocking it (as discussed in The Times last week ).

The shift may also represent the Administration’s willingness to jettison its belief that contact with the US should be given only as a reward for change. That hasn’t got it anywhere with Iran, or Cuba.

Of course, it is hard to argue that the European engagement has done much better. Iran has refused to give up enrichment, which it says is to make reactor fuel, but which some suspect is meant to make fissile material for weapons. Nor has it answered the questions of the International Atomic Energy Agency, particularly about its work pre-2003.

But it has been keen to keep the talks going and to avoid worse sanctions from the UN Security Council. Nor has it quit the Nuclear Non-Proliferation Treaty, although its evasions have brought much sharper criticism from the IAEA. For all the novelty of the US presence at these talks, the only point that matters is the Iranian response to the package of rewards offered several weeks ago. You can’t say expectations are high. “I don’t know,” said Condoleezza Rice, Secretary of State, when asked if Iran would give a positive response. Her French counterpart, Bernard Kouchner, was even gloomier, saying that Iran’s coolness so far was “not surprising, a bit sad”, although its readiness to talk further was encouraging.

“We are waiting for an opening. I talked to [the Iranian Foreign Minister Manouchehr] Mottaki and he was open, but open to what? That is always the case. We talk and talk with the Iranians, but it’s always disillusion,” said Kouchner, speaking in English. That is the authentic flavour of this marathon: never outright failure, or success, yet the threat too serious to walk away. A third-rank official from the waning Administration is not going to break that deadlock. Better look to Barack Obama’s visit to the Middle East and Europe next week to inject a sense of US purpose that these talks now lack.

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