The Taoisaeach tonight warned Northern parties that it would be a "huge mistake" to pass up this opportunity for an agreed settlement "in the expectation that another equally attractive one will present itself within a short time-frame".
In an address to the students in Trinity College Dublin, Mr Ahern said: "If this opportunity is squandered, it will have consequences both in terms of the time that elapses before we can again seek to restore devolved government in Northern Ireland."
He said neither he nor Mr Blair were in favour of parking the process.
"We hope in the coming days to finalise our proposals."
"We will ask the parties to give them careful consideration; to seriously reflect on the opportunity that is now available to address and resolve all of the issues that have obstructed the achievement of a stable dispensation in Northern Ireland; and to take serious account of the opportunity costs if the current window is allowed to close without a constructive outcome," he said.
The Taoiseach warned that the prospect of ending IRA activity and capability could be lost because of what he called "unrealistic thresholds of visibility".
He said it would be entirely counter-productive if people made unreasonable demands that carry a resonance of humiliation for any side.
Earlier the Taoiseach gave his strongest indication yet that the IRA may be on track to decommission its weapons by the end of the year.
"We are so near," he said. "But I fear some think there is some tactical advantage to be gained by long-fingering this.
He said a report by RTÉ this morning claiming that behind-the-scenes talks with the two Governments, the DUP and Sinn Féin included the prospect of IRA decommissioning by the end of the year should not be discounted. "It is very near the mark."
The Taoiseach said people would be amused if they knew the issues currently preventing progress.
"We are within a fortnight of making a decision," he added. "So we can crack the outstanding points and do it comprehensibly and successfully or decide, having almost got there for the third time in a two-year period, to leave it aside."
He said that if negotiations were allowed to drift now, elections scheduled for next year in both Britain and Northern Ireland would push the whole process back to 2006.
"That would be a real tragedy - a real mistake," he added.