BELFAST, Northern Ireland (AP) _ With two key parties sticking to incompatible positions, Northern Ireland's rival politicians failed Wednesday to meet a midnight deadline for saving the 1998 Good Friday peace accord.

British Prime Minister Tony Blair launched the negotiations this week in hopes of winning a long-overdue agreement to form a new Protestant-Catholic government for Northern Ireland, the central plank of an accord reached on Good Friday last year.

The negotiations passed the midnight deadline and continued into the early hours Thursday at Stormont, center of British administration in Northern Ireland.

The talks reached their 18th straight hour at 3 a.m. (10 p.m. EDT Wednesday) without the publication of a long-awaited report by the disarmament commission established under the accord.

The report would formally assess the prospects for winning the gradual disarmament of the IRA.

Despite mounting pressure from both Blair and Irish Prime Minister Bertie Ahern since the latest talks began Monday, the IRA's allied Sinn Fein party was refusing to give any firm assurance that the outlawed group would start to disarm by any fixed date.

The Ulster Unionists, chief representative of Northern Ireland's British Protestant majority, have demanded that commitment before they will accept Sinn Fein members in two of the government's 12 posts.

Indeed, their position remained that the Irish Republican Army must start disarming at the same time as the government's formation. The Ulster Unionist leader, David Trimble, has already been elected to lead the government.

``We ought, in the words of the leader of Sinn Fein-IRA, Gerry Adams, jump together,'' said Ulster Unionist deputy leader John Taylor, who was shot 16 times in the face and body by an IRA assailant in 1972.

``In practical terms, that means they give up some of their illegally held armaments at the same time as we let them into the Cabinet,'' said Taylor, who rated the chance of that being agreed to by Wednesday's deadline as very low _ ``4 percent.''

President Clinton, meanwhile, urged the British and Irish to ``give peace a chance,'' telling reporters after a speech in Chicago that he stands ready to become personally involved in the deadlocked talks in Belfast _ if he is needed.

``I will do whatever I can to be helpful. We're moving forward and I'm hoping for the best,'' said Clinton.

Clinton also suggested that the Ulster Unionists ought to let Sinn Fein into the new government first and then see whether the IRA lays down all weapons by May, the only disarmament deadline in the Good Friday accord.

The U.S. president spoke with Blair by telephone for about 10 minutes. White House aides said the two leaders promised to get back in touch later in the day to discuss the situation further.

The latest Blair-Ahern objective, according to both governments, was to wring a cast-iron guarantee from Sinn Fein that the IRA _ now nearly two years into an open-ended truce _ would fulfill the accord's expectation of total disarmament by May 22, 2000.

The IRA has hidden many tons of weapons in expertly concealed bunkers in the neighboring Irish Republic.

Under this scenario, the first act of IRA disarmament would be required between September and December, after the government was formed and given powers by the British government, which took direct responsibility for Northern Ireland after abolishing its Protestant-dominated government in 1972.

For Sinn Fein's Adams and the Ulster Unionists' Trimble, the compromise sought by the prime ministers would mean huge personal political risks.

Trimble, a Nobel Peace Prize laureate, has so far survived an almost even split in Ulster Unionist ranks over his support for the accord. He already requires police guards when walking in his own constituency. A hard-line challenge to his leadership is considered likely if he accepts Sinn Fein as government partners before the IRA starts to disarm.

Adams has been determined to avoid a similar split among his own more volatile colleagues.

The last split in 1997 produced a dissident IRA gang that committed the worst terrorist attack in Northern Ireland history, the August car bombing in Omagh that killed 29 people.