The leader of Northern Ireland's major Protestant party said Tuesday he wasn't prepared to sustain the province's power-sharing administration unless the Irish Republican Army delivered on its promise to disarm.

Though lauded by governments in London, Dublin and Washington, Monday's carefully choreographed IRA move left the Ulster Unionist Party unimpressed -- and the province's 20-month-old administration still in danger of extinction within days.

The announcement by disarmament officials that the outlawed IRA had "proposed a method for putting IRA arms completely and verifiably beyond use" left observers and politicians debating its significance.

The optimists, mostly Catholics, argued that the IRA was about to start scrapping its tons of stockpiled weapons, an issue that has dogged the peace process for years. The skeptics, mostly Protestants, said the IRA's move was a cynical bid to divert pressure back to the Ulster Unionists, who would bear the blame for the coming government breakdown.

Ulster Unionist leader David Trimble, speaking before a meeting of his party's 28 members of the Northern Ireland legislature, said the IRA would show which side was right in the coming crucial days.

"Decommissioning isn't issuing statements, decommissioning is destroying weapons. It hasn't happened. That's why we have a crisis," Trimble said.

Trimble, a Nobel Peace Prize laureate who has twice overcome substantial Protestant hostility to form administrations that included the IRA-linked Sinn Fein, fueled the crisis last month by resigning as the senior Protestant minister. He said the days when he took political risks based on IRA words was over.

"We have taken risks, we have gone forward, we have formed the administration not once but twice on the basis of expectations, and both times we were let down. That simple fact cannot now be avoided. I'm not going to do it a third time," he said.

Behind the rhetoric, Trimble faces an uphill struggle to be re-elected as the Protestant leader of the four-party administration. It was forged under terms of the Good Friday peace accord of 1998 that sought to end three decades of bloodshed here.

Without Trimble or another Ulster Unionist serving as first minister, the entire 12-member Cabinet and its underlying legislature must be suspended or dissolved by Britain by next Monday.

"The Ulster Unionists need to put forward one of their number to be first minister so that we can get on with working the power-sharing institutions," said Sinn Fein's Martin McGuinness, a former IRA commander who has served as education minister in the Trimble-led coalition.

McGuinness accused Trimble of rejecting the disarmament commission's "breakthrough report." He said this was "a mistake of monumental proportions."

If Trimble were to offer himself for re-election later this week, complex voting rules within Northern Ireland's 108-member legislature mean he couldn't be confident of success. He would require support from more than half of both the Catholic and Protestant sides of the house.

While most Catholics say they would vote for him, Protestant representatives are split almost evenly between Trimble supporters and hard-line critics, who oppose a process that has brought Sinn Fein a slice of power.

Among Trimble's Ulster Unionist colleagues in the legislature, a crucial few oppose his policies and have already declared they would vote against him.

Many more Ulster Unionists are upset with last week's joint British-Irish document designed to encourage an IRA arms move. It contained promises from Britain to slash its military forces further, strengthen its plans for reshaping Northern Ireland's mostly Protestant police force and grant an amnesty to IRA fugitives.

Britain and Ireland welcomed the news that the IRA had agreed with disarmament officials on a secret method for putting weapons beyond use. Both said they hoped the disarmament commission would quickly confirm that the process had begun.

In Washington, where the Bush administration has adopted a much more hands-off policy on Northern Ireland than its Clinton predecessor, the State Department also welcomed Monday's statement.

"We do see this as a significant step toward the Good Friday agreement's agreed goal of putting paramilitary weapons completely and verifiably beyond use," said spokesman Richard Boucher.