A failure to break the political deadlock in the North before the end of this month could impose an "intolerable" two-year delay in restoring the Assembly and Executive, the Taoiseach, Mr Ahern, has said.
Such a situation would be "extremely unhelpful" to the peace process.
He said only weeks remained before the current opportunity for an agreement between the parties lapsed.
With Britain set to take the presidency of the EU and G8 next July, the Taoiseach said there was only a "small opportunity" to restore power-sharing and "keep well clear" of British local elections next spring.
He also cited the strong possibility of a British general election in the middle of next year. "That brings us into 2006, and the elections were in November 2003. That just gets into an intolerable position. It is correct to focus on the limited opportunity."
However, Mr Ahern said he agreed with remarks made by the Northern Secretary, Mr Paul Murphy, who said yesterday that "fundamental political change" was within grasp.
"I think that all of us would agree that we've only a matter of weeks. I said this yesterday. I think what Paul Murphy said today; I agree with. I think that people are focusing their minds, and their minds very diligently, and trying to make progress now."
Irish sources have said the end-October deadline was necessary to allow time for the "sequencing" of IRA decommissioning and other acts before next May's UK elections.
A delay of even a fortnight would mean that not enough time would exist for the agreed confidence-creating measures to be carried out in an orderly fashion, the sources say.
The two governments may yet publish the detailed terms of a proposed final deal this month if the Northern parties balk at signing up.
Meanwhile, the Minister for Foreign Affairs, Mr Dermot Ahern, will meet with Mr Murphy tomorrow.
An Ulster Unionist Party delegation will be in Dublin on Thursday for meetings with the Minister.