Mr David Trimble has dismissed Mr Jeffrey Donaldson's plan for decommissioning and devolution as unrealistic. He said it was a step backwards.
The anti-agreement MP has sent his proposal to delegates who will attend today's Ulster Unionist Council meeting. They will vote on Mr Donaldson's plan and on Mr Trimble's proposal to return to government.
Mr Donaldson is recommending that the Ulster Unionists reenter the Executive only after confirmation that the Provisional IRA has commenced credible and verifiable decommissioning "within an agreed timetable". In the meantime, the Assembly should develop policy and increase the accountability of the administration in the North.
Mr Donaldson discussed his plan with his party leader yesterday. Mr Trimble rejected it as "nothing new".
He said: "There isn't anything new in this. On a number of occasions over last year proposals very like this were explored. From the response we got from other parties, there wasn't much mileage in them.
"If the UUP were to go back to ideas of some sort of phased implementation, other parties would regard it as simply moving backwards and adopting a unionist wish-list. There isn't really much prospect of this working."
Mr Trimble said Mr Donaldson's proposals could cause some confusion among those UUC members who had not yet made up their minds on how to vote. He said re-entering the Executive represented an opportunity to make real progress but admitted that the Provisional IRA offer "carries with it some element of adventure".
However, he said the UUP would still have options after reentering government as the process required its confidence. "If confidence is not being sustained, then the process cannot be sustained."
Many observers believe Mr Trimble's leadership is on the line today but he would not concede that the vote was "a make or break situation" for the political process.
"This process is a darned sight more robust than most people think," he said.
He hoped the party would unite in support of policy if his motion was accepted. "We hope that the lessons of the damage disunity causes will have been learned."
Mr Donaldson said his alternative plan was a "genuine and sincere attempt" to avoid division in the UUP, as there had been deep unease within the party over the Provisional IRA statement.
"Our twin objectives are sustainable devolution and disarmament. But it has to be government based on democracy and committed to democracy."
Mr Martin McGuinness said the UUP held the key to the future and would decide if the agreement survived or failed. The Sinn Fein MP appealed to the UUP to join his party in working for the future.
He said many unionists appreciated that republicans had travelled "a long and difficult journey of change" and were genuinely attempting to reach an accommodation with their community.
"I realise that the last number of years in particular have been a time of uncertainty for unionists. I and my colleagues have tried to offer certainty. We have done so not just in words but in deeds. Inclusivity, equality and mutual respect is the only way forward."
The Alliance leader, Mr Sean Neeson, urged the UUC to support Mr Trimble. "Never before in our history has the future of so many depended upon the votes of so few. It is vital the Ulster Unionists do the positive and responsible thing and listen to the people."