Mr David Trimble is to seek clarification on three points before deciding whether he will recommend a return to government to his party's 860-strong Ulster Unionist Council on Saturday.
A UUP spokesman told The Irish Times that one of the issues the leadership wanted clarified was the exact meaning of the IRA's statement offering to put its arms "beyond use" and allow international observers to inspect a number of its weapons dumps.
A further point of clarification will concern the precise modus operandi of the two international arms inspectors, Mr Cyril Ramaphosa, of the African National Congress, and Mr Martti Ahtisaari, the former Finnish president. Mr Trimble is expected to meet Mr Ramaphosa and Mr Ahtisaari on their first official visit to Northern Ireland today or tomorrow to question them on how they envisage carrying out their task.
Finally, the UUP is to press the British government for assurances on other "issues of concern". These are likely to include retention of the RUC name and the flying of flags from public buildings.
Mr Trimble said that only once these matters were clarified to his satisfaction would he be able to recommend his party's re-entry into government with Sinn Fein. "If I am to table a motion to return to government - and I haven't said I will - it will depend on having my expectations fulfilled in the course of the week", he added.
There has been speculation that some senior UUP figures are unhappy with Mr Trimble's decision to call the UUC meeting. According to a report in Sunday Life, the party president, Sir Josias Cunningham, opposed this, pointing to the gravity of the risk Mr Trimble was taking.
Mr Jeffrey Donaldson warned that it would be a mistake to return to the power-sharing Executive without establishing first what the IRA offer entailed, while Mr William Thompson, UUP MP for West Tyrone, described Mr Trimble's decision as "premature".
The deputy leader of the Democratic Unionist Party, Mr Peter Robinson, told BBC Radio Ulster's Inside Politics programme that Mr Trimble would win a UUC vote in favour of the deal.
Asked whether in that case he envisaged a "realignment" within unionism, with anti-agreement Ulster Unionists joining the DUP, Mr Robinson said that there clearly needed to be "much greater cohesion and potency" among anti-agreement forces. "This is without doubt a defining moment in unionism", he added.
Meanwhile, Sinn Fein's chief negotiator, Mr Martin McGuin ness, has insisted that the arms inspections to be carried out by Mr Ramaphosa and Mr Ahtisaari would go ahead "come what may" and were not dependent on reinstatement of the power-sharing Executive.
Now that the impasse over decommissioning had been "finally resolved", unionists were seizing on other issues, such as the flying of flags and the name of the RUC, to block further progress, Mr McGuinness told ITV's Dimbleby programme.
After a brief meeting with the British Prime Minister, Mr Tony Blair, in London today, Mr Ramaphosa and Mr Ahtisaari will travel to Belfast to meet the Minister for Foreign Affairs, Mr Cowen, and the Northern Secretary, Mr Peter Mandelson.