Leading article: A reversal that is as welcome as it is timely

All diplomacy contains ambiguity, and it is possible that there is less to the U-turn signalled yesterday by the US Secretary of State, Condoleezza Rice, than appears at first sight. After all, what Ms Rice actually said was that the United States was prepared to join talks with Iran "if" - and that "if" might be all-important - Tehran suspends its uranium-enrichment programme. Given Tehran's intransigence hitherto on this very subject, we may be contemplating a clever way of appearing flexible, which is designed to achieve nothing at all.

There is, however, another, far more optimistic gloss that can - and should - be placed on the statement that Ms Rice delivered without advance notice from Washington yesterday. In this interpretation, the "if" was as much for the benefit of the home crowd as for the Iranians. For months, the American public has heard only aggressive, no-holds barred statements from the administration in relation to Iran. The bottom line has always been that force will not be ruled out.

This hard line was less in evidence yesterday. Indeed, the careful wording of Ms Rice's announcement had a very different feel from almost any foreign policy move that has borne the signature of the Bush administration. It may not be far-fetched to see this, rather than the instant ridicule that issued from the White House, as Washington's real response to the exotic treatise sent by President Ahmadinejad to President Bush three weeks ago.

What Ms Rice is now proposing, even allowing for the caveats, is an almost complete reversal of US policy towards Iran as it has stood for more than 25 years. Having demonised Iran since the US embassy siege of 1979, Washington says it is ready to join "direct multilateral" talks with Iran on its nuclear programme. This is something less than de facto diplomatic recognition: the US would join talks as a participant with others, and only the nuclear issue would be on the table. That the talks would be direct, rather than through an intermediary, however, is a real departure for US policy and the first sign of a crack in the US position.

Ms Rice made her statement on the eve of talks in Vienna at which foreign ministers of the five permanent members of the UN Security Council, and Germany, are expected to finalise new proposals to put to Iran. Until yesterday, the fear among the three European representatives was that a continued hard line from the US would frustrate efforts to form a united international front. Ms Rice's determination, as she put it, to "give diplomacy its very best chance" and her explicit support for Europe's negotiation efforts signal that if anyone has made a concession, it is the US and not the European "three'.

The first move towards the European position was made by President Bush at the start of the year when he expressed support for the British, French and German overtures. In recent months, however, that support seemed to waver, as the US forced the pace on bringing the nuclear issue to the UN. The tone and content of Ms Rice's latest statement suggests that Washington may be ready to make a new start, following the Europeans in preferring incentives as a better way to encourage Iran's compliance.

At such a hopeful moment, it might be ungracious to point out that the US change of policy, however elegantly executed, is evidence of weakness in Washington, not strength. An enfeebled George Bush presides over an administration lacerated by its involvement in Iraq. His Republican Party faces congressional mid-term elections in a fractious and demoralised state. More sabre-rattling might earn him cheap populist points, but its usefulness wears off. Another enemy is a luxury this White House can no longer afford.