The leaders' two-day summit outside Belfast starting Monday could conclude with Mr. Bush's endorsement of a proposed new peacemaking deal for Northern Ireland, where a 1998 peace accord has survived a string of political crises but requires major repair work.
Blair, a stalwart ally in Bush's war with Iraq, hopes presidential backing will strengthen his hand when he publishes his government's new Northern Ireland plans by Thursday — the fifth anniversary of the Good Friday accord.
That landmark pact sought to forge a compromise-minded Northern Ireland in which British Protestants and Irish Catholics worked together in a new government and a reformed police force.
It hasn't quite worked out that way. Protestants deeply distrust hard-liners from Sinn Fein, the Irish Republican Army-linked party, and their power-sharing coalition has been on ice since October. Sinn Fein refuses to support the police despite three years of negotiations.
Overshadowing everything is the IRA, an underground organization officially committed to Northern Ireland's overthrow but observing a cease-fire since 1997. It has been accused of a raft of truce-violating offenses ranging from weapons smuggling to gathering intelligence on potential targets.
The major Protestant party, the Ulster Unionists, insists Sinn Fein can't sit again at the Cabinet table until the IRA fades away. Moderate Catholics dislike the Ulster Unionists' ultimatums but agree that Sinn Fein's position of wanting to help run the government, but refusing to support law and order, is contradictory.
Irish Prime Minister Bertie Ahern, who plans to join Bush and Blair on Tuesday, publicly backs the Ulster Unionist view. Ahern says the IRA should issue a statement making it clear that the outlawed group won't resume bombing and shooting.
Ahern and Blair also expect the IRA to resume disarming, a process that under the Good Friday pact was supposed to be completed three years ago. The IRA started scrapping weapons in October 2001 but stopped in April 2002.
Ulster Unionist leader David Trimble said he expected Bush to take the same line on the IRA as he does with Saddam Hussein.
"George Bush is certainly not weak on the question of democracy, and on the questions of terrorism, so I think one would expect the president would come with a very clear view of the situation," said Trimble, who shared the 1998 Nobel Peace Prize with moderate Catholic leader John Hume.
The Bush-Blair summit is also supposed to discuss prospects for reviving a peace process between Israel and the Palestinians. Blair has previously held up the recent Northern Ireland experience as a model to inspire peace in the Middle East.
Bush's trip should bear little resemblance to the three high-profile visits paid to Northern Ireland by his predecessor, Bill Clinton, when largely Catholic crowds in their tens of thousands turned out to cheer his appearances — and Protestants largely bit their lips.
Clinton's interest in Northern Ireland was a bonanza for Sinn Fein. The party was a political pariah before Clinton gave Sinn Fein leader Gerry Adams a U.S. visa in 1994, then dropped the longstanding ban on Sinn Fein fundraising in 1995.
But on Monday night, Sinn Fein says it's going to join protests against the Iraq war at the expected summit venue, Hillsborough Castle outside Belfast. The party's Dublin section said it would bus up activists to join left-wingers from the Stop the War Coalition, whose posters label Bush as "War criminal in Belfast."
Northern Ireland's moderate Catholic party, the Social Democratic and Labor Party, criticized the idea of mixing Iraq war planning with Northern Ireland peacemaking.
"I cannot disguise my personal unhappiness at this, given my own opposition to this war and my concern for the integrity of our own peace process," said party leader Mark Durkan.
Until now, Bush has shown little interest in Northern Ireland. Hands-on U.S. involvement has been delegated to Richard Haass, a senior State Department official, who travels regularly to Belfast.