The Taoiseach and the British Prime Minister will spend today at Hillsborough Castle seeking a deal to keep the North's political institutions in operation until talks resume after the British election.
Mr Ahern is almost certain to cancel his planned six-day visit to Japan, due to begin today, to join round-table discussions in Belfast.
He is doing this even though hopes for a comprehensive deal on the outstanding issues of decommissioning, demilitarisation and policing have now all but evaporated for the time being, according to sources in both governments.
It is understood "an intermediate deal" would involve the Provisional IRA re-establishing contact with Gen John de Chas telain's international decommissioning body in return for movement by Britain on demilitarisation in south Armagh and UUP leader Mr David Trimble lifting the ban on Sinn Fein ministers attending North-South Ministerial Council meetings.
However, to ensure even limited movement from republicans on decommissioning, the British government must give some commitments on demilitarisation, and the dispute over the new police force must also be defused, at least temporarily.
Today's talks will concentrate on an attempt to achieve limited but sufficient progress to ensure the power-sharing Executive, North-South institutions and British-Irish body can survive beyond the summer.
It is understood that Mr Tony Blair and the Taoiseach will hold bilateral talks with Sinn Fein, the SDLP and the Ulster Unionists in the morning before moving to a round-table session involving all the pro-agreement parties at lunch-time.
Sources said there would be more bilaterals in the afternoon followed by another round-table discussion in the evening.
British government sources warned against optimism about a major breakthrough. One source predicted there would be no dramatic ending to the stalemate. "At best, all that is possible would seem to be a holding deal that would take us to the other side of the elections and save the institutions from suspension."
The importance the Government attaches to averting a breakdown is illustrated by the decision that the Minister for Justice, Mr O'Donoghue, the Attorney General, Mr Michael McDowell, Minister of State Ms Liz O'Donnell, and the senior officials involved in the process will travel to Hillsborough.
The talks are expected to go on late into this evening, and a second day of meetings at Hills borough has not been ruled out.
To avoid a breakdown in the institutions, there must be sufficient movement on decommissioning to allow Mr Trimble to convince his party that it should continue to participate in the Executive, the North-South and east-west bodies.
In the absence of agreement, the governments may put forward their own ideas on how to minimise any sense of political vacuum during what is expected to be a bitterly fought election campaign in Northern Ireland.