Tony Blair is to call for dialogue with Iran and Syria to secure peace in the Middle East, as Defence Secretary Des Browne says change is "under way".
Tony Blair is set to make a major foreign policy speech
The prime minister believes the two states should be warned of the consequences of failing to help.
In a major foreign policy speech in London he will also defend the UK's close relationship with the US.
The Syrian ambassador to the US told the BBC his country was willing to "engage" with the US and the UK.
Mr Blair will say that a "whole Middle East" strategy is needed to combat global terrorism and extremism as evident in Iraq .
"A major part of the answer to Iraq lies not in Iraq itself but outside it, in the whole of the region where the same forces are at work, where the roots of ...global terrorism are to be found, where the extremism flourishes."
He said it was necessary to start with "Israel/Palestine" as it was "the core". Progress was also needed in Lebanon, Iraq, and Iran.
Ahead of Mr Blair's speech, his defence secretary played down suggestions the US mid-term elections were behind an apparent change of UK policy on Iraq.
"Change has been under way for some time now and it distorts the reality to suggest that that change is predicated upon a change in American politics," said Mr Browne.
He added: "Throughout the conflict, for example, we've been calling on Iran and Syria to do more to stop the flow into Iraq of foreign fighters, bomb making equipment and knowhow - and we will continue to talk to all of Iraq's neighbours."
The White House has already indicated it would consider talking to Iran and Syria - previously described by President Bush as part of an "Axis of Evil" - about the future of Iraq.
Syria's Ambassador to the US, Imad Moustapha, told BBC Radio 4's World at One that his country was willing to engage.
Price of peace
"In one way or another, Syria wants to become a part of the solution to the problem. We are willing to engage and we can help - I'm not claiming we have the magical wand - we can help play a constructive role.
"We have played a constructive role in the past. Syria has invited Israel time and again to re-engage in a peace process."
He added that for such assistance "the price should be very clear - we want a comprehensive, fair and honourable Middle East settlement".
Mr Blair will address the Lord Mayor's banquet at the Guildhall stressing the need to "make clear" to Syria and Iran how they can help make peace in the Middle East, an aide said.
He will add that the only British foreign policy that could work is one based on "strong alliances".
'With or against us'
"For that reason, our partnership with America and our membership of the EU are precisely suited to Britain," he will add.
"For that reason anti-Americanism or euroscepticism are not merely foolish, they are the surest route to the destruction of our true national interest."
The US death toll in Iraq stands at more than 2,800 troops
In the US, White House chief-of-staff Josh Bolten said "a fresh approach" was needed on Iraq.
Its Iraq Study Group is due to give its recommendations on US strategy in Iraq by the end of the year.
President George W Bush is meeting the panel on Monday, and Mr Blair will talk to it via video link on Tuesday.
The panel reportedly thinks that "staying the course" is an untenable long-term strategy, and is said to have been looking at two options.
One is the phased withdrawal of US troops, and the other is to increase contact with Syria and Iran.
A Downing Street spokeswoman said Mr Blair would ensure the members of the panel were "fully briefed on UK ideas" when he spoke to them.
British officials had been in contact with the panel since it began, and the prime minister's intervention was "a natural extension of that", she said.
Shadow foreign secretary William Hague welcomed Mr Blair's engagement with the US panel, stressing the need for "heavy British involvement" in the reassessment of current thinking.
But he told BBC News hopes of involving Iran and Syria in the short-term could prove "naive".
"We have to make the most of our friendships and build on our friendships with the moderate Arab nations of the Middle East," he said.
Liberal Democrat leader Sir Menzies Campbell criticised Mr Blair's willingness to appear before the US panel to discuss ideas for strategy in Iraq while refusing to do the same in the UK.
"We need a fresh strategy based on British priorities, not one that relies on the outcome of an American inquiry."
He suggested a "new approach with phased withdrawal at its centre is essential" and pushed for Iran and Syria to be involved.