BELFAST, Northern Ireland -- Sinn Fein must be kicked out of Northern Ireland's administration within a week, or Protestants will scuttle the entire experiment in Protestant-Catholic power-sharing, First Minister David Trimble warned Britain in a high-risk showdown Tuesday.

Trimble said his Ulster Unionist Party would withdraw if Britain didn't formally recommend that Sinn Fein, the Irish Republican Army-linked party, be expelled because of alleged IRA spying.

A withdrawal by the Ulster Unionists would bring the nearly 3-year-old coalition with two Irish Catholic parties crashing down. Britain could forestall a collapse by stripping power from local hands -- a step taken in 2000 and 2001 that kept the coalition intact through previous crises.

"We are giving him one week, and I do think we are being very generous," Trimble said after talks with Prime Minister Tony Blair.

Blair, loathe to take any action that would upset the IRA's 1997 cease-fire, scheduled separate talks starting Wednesday with Irish Prime Minister Bertie Ahern, Sinn Fein and the larger moderate Catholic party in the coalition, the Social Democratic and Labor Party.

But Blair's minister for Northern Ireland, John Reid, stressed they had to balance the administration's survival with wider peacemaking goals.

"It is a very difficult and grave situation. ... But at the moment it isn't easy to see how we find our way through," said Reid, who retains considerable power in the province.

Reid could either return sole authority to Britain or, as Trimble wants, introduce a motion into Northern Ireland's legislature on Monday seeking a vote to drive Sinn Fein from office.

Can be thrown out

Majorities on both the British Protestant and Irish Catholic sides of the house would have to vote in favor of booting Sinn Fein from its two posts in the 12-member administration.

Under the 1998 Good Friday pact, a party can be excluded from power if it is in breach of its commitment to observe "exclusively peaceful and democratic means."

Protestants moved to force Sinn Fein from office after police raided the homes and offices of party activists Friday and allegedly seized stacks of pilfered British documents provided by a sympathetic civil servant.

Among the documents, police said, were details of potential IRA targets.