Before leaving Beirut, David Miliband told suspicious Lebanese politicians yesterday that they had no cause for alarm over Britain's apparent rapprochement with Damascus. Talks with President Assad had been on an “honest and serious basis” and he had made clear to Syria its choices if it wished to end its isolation.

His assurances were directed as much at Washington as to Beirut. Some Lebanese are fearful that the West may be ready to play down the investigation into the murder of Rafik Hariri, the former Lebanese Prime Minister, in return for Syrian help on intelligence, Middle East peace talks and curbing the flow of weapons and fighters into Iraq. The Bush Administration has long regarded Syria as an obstacle to regional peace, an abetter of violence by Hamas and Hezbollah and an ally of Iran that extends Tehran's malign influence.

That assessment is not wrong. But the ostracism of Damascus overlooks two crucial recent changes: Syria's clear attempts to break free of an Iranian alliance that it finds increasingly suffocating; and the arrival in January of a new administration in Washington. Mr Miliband is determined to do what he can to help to bring Syria in from the cold to give Barack Obama greater flexibility in looking afresh at US initiatives.

He has been wise not to expect too much. Tony Blair's mistake, during his ill-judged foray to Damascus in 2001, was to overestimate the power of his persuasion and overlook long-held Syrian positions and the entrenched interests of hardliners around Mr Assad. Syria saw no reason to drop its support for Hezbollah, distance itself from Iran or expel exiled Hamas leaders from Damascus. Since 2001, things have changed - and not to Syria's advantage. Hariri's killing, the UN investigation and Syria's forced withdrawal from Lebanon have left Damascus isolated, an uncomfortable position exacerbated by the growing hostility among other Arab states to the alliance with Iran.

Syria has therefore taken a number of steps to try to reopen lines of communication to the West. President Assad flew to France in the summer in an attempt to mend fences. He has now, for the first time since Lebanon's independence from France, opened formal diplomatic relations with Beirut. There has been a tightening-up along the Iraqi border (though not enough to prevent the recent US-Iraqi attack on a Syrian border town). And in a clear attempt to woo Washington, Syria restarted indirect talks with Israel, via Turkey, in May.

Mr Miliband is right to try to build on this - as well as on the other wholly positive aspect of Syria's secular Constitution, its religious tolerance and the shelter that it has given to Iraqi Christians. He is also right to make it clear there can be no deal to halt the Hariri investigation in return for warmer relations. The West, in any new dialogue, should urge Syria to take bolder steps in talks with Israel, turning a propaganda move into a serious negotiation that could, possibly, lead to the return of the Golan Heights. It should also make plain that if it continues as a proxy of Iran, arming Hezbollah and encouraging Hamas, it cannot expect to be taken seriously either by Israel or by the West. Syria has too often tried to make itself central to regional peace by playing the spoiler. It has few cards left to play now. It is time to play a trump - principled, pragmatic co-operation.