The British government, which expects to secure the backing of the US for the change, is to offer a reworked resolution that would give Iraq "a little more time" and set a deadline on which most of the UN security council could agree.
An extra few weeks would push war back to the end of the month. Such a delay may be acceptable to the US, because its military timetable has been thrown into disarray by Turkish intransigence over troop movements.
A US official said: "We may add or subtract to the resolution but we will not do anything that detracts from the substance of the resolution." The thrust of the resolution is to authorise war against Iraq.
The new-found willingness to compromise amounts to an admission that Britain and the US cannot win a majority in the security council for the resolution in its present form. It states that the Iraqi president, Saddam Hussein, had had his "final opportunity" to disarm.
When the resolution was tabled last week, Britain and the US indicated that it was set in stone and the White House spokesman, Ari Fleischer, said he expected a vote on the resolution "in short order".
But only Britain, the US, Spain and Bulgaria support the resolution, and arm-twisting has so far failed to move the other 11 security council members. France, Germany and Russia, after a hastily con vened meeting in Paris yesterday, issued a joint statement signalling that they will block the resolution.
The compromise resolution is expected to be floated when foreign ministers representing the 15 security council members meet in private in New York tomorrow after a report by the UN chief weapons inspector, Hans Blix.
The US and Britain are hoping that Mr Blix's assessment will boost their position by concluding that Saddam has fallen far short of his disarmament obligations.
Speaking to reporters at the UN yesterday, Mr Blix offered a measured assessment, saying Iraq had been complying in some areas but that all of Iraq's biological weapons had not been accounted for.
The US secretary of state, Colin Powell, insisted in a speech last night that Saddam had ordered the construction of new illegal missiles and was hiding chemical and biological weapons along Iraq's borders.
He said that in late January, the Iraqi intelligence service had moved banned chemical and biological materials to remote areas of the country near the Syrian and Turkish borders. Mr Powell also claimed that banned materials were being moved every 12 to 24 hours to avoid detection by the inspectors.
Tony Blair told the Commons yesterday that he was confident of securing support from the council. This confidence stems in part from reports from the six swing countries - Guinea, Cameroon, Angola, Mexico, Chile and Pakistan - that they might back the resolution if it was changed to allow more time and set clear tests for President Saddam.
If five or all six swung behind the resolution, the British and US predict that France, Russia and China would then be likely to abstain rather than exercise their vetoes.
The Russian foreign minister, Igor Ivanov, repeated to Mr Blair at Downing Street yesterday morning what he has been saying in public: that Russia would neither vote for nor abstain on the resolution in its present form, implying that it would exercise its veto.
The new timetable could see the diplomatic phase end around the Middle of March, followed by a short gap before military action.
Last night the Russian president, Vladimir Putin, spoke to the Canadian prime minister, Jean Chrétien, about a compromise resolution proposed by Canada under which Iraq would be set a number of deadlines for compliance.
The first deadline of February 28 floated by the original Canadian "non-paper" has been re vised to March 31. The Russian ambassador to the UN, Sergei Lavrov, expressed interest in the Canadian proposal on Tuesday, saying that the idea was "very close to our own approach".
· Two Iraqi security guards at their UN mission were last night ordered to leave the US for alleged spying. Iraq's UN ambassador, Mohammed al-Douri, said the men, who had the rank of attache, were given 72 hours to leave the country.