He's been called "the most patient man in Ulster," and former Senate majority leader George Mitchell earned the title again today as he agreed to come back next week for yet another try at breaking the long stalemate in the Northern Ireland peace process.

The normally unflappable Mitchell was reportedly furious this morning when leaders of the Ulster Unionists, the largest Protestant party, once again refused to accept the cautious, step-by-step plan he has worked out with political leaders on the Roman Catholic side. Rather than throw up his hands in defeat, however, Mitchell told the parties to take the weekend off, "reflect on the magnitude of the decisions they have to make," and join him for more talks starting Monday.

All week there had been signs of an impending breakthrough. Although Mitchell has imposed a news blackout on the talks, there were reports that the Irish Republican Army and its political wing, Sinn Fein, had agreed to take some new steps toward the IRA's eventual disarmament. David Trimble, head of the Ulster Unionists, was reportedly impressed with the IRA suggestions.

On Thursday, Trimble set out to sell the new formula to his party's leadership. After an exhausting day of meeting party members in small groups, he reported that he did not have enough support to sign a deal--prompting Mitchell to call the weekend recess.

Despite the setback, there was a general tone of cautious optimism here about the progress Mitchell has made this fall. "We are on a knife edge," said Peter Mandelson, the British cabinet secretary responsible for Northern Ireland. "But we are on a knife edge with a lot going for us."

Mitchell came back to Northern Ireland somewhat reluctantly when the governments of Britain and Ireland pleaded with him to head a review of the stalled efforts to implement the ambitious 1998 Good Friday peace accords. Mitchell said the review would last about a month. That was 10 weeks ago.

As usual, the dispute in this British province of 1.6 million people centers on government and guns.

The predominantly Catholic republican side--those who want Northern Ireland to break its ties with Britain and merge with the Republic of Ireland to the south--has supported the Good Friday agreement because it creates a new local government for the province, with significant Catholic involvement.

The predominantly Protestant unionist side--those who want to retain the political union with Britain--has refused to endorse the new local government until the IRA starts to surrender some of the weapons in its extensive arsenal.

Last July, when the new Northern Ireland Assembly was scheduled to open for business, the Ulster Unionists boycotted the session, and the assembly collapsed in a flurry of taunts and insults.

Mitchell's strategy has been to plan a sequence of small, even minuscule, steps forward, with each step leading to a reciprocal effort by the other side.

Among other things, he evidently persuaded the IRA to agree to meet regularly with the international committee supervising disarmament of the various sectarian militias here. That would be a major step for the IRA, which has always said it would never give up its weapons.

Mitchell is also said to be working out a "fail-safe" mechanism so that neither side will be left behind as the peace process moves ahead. Reports here say that he proposed implementation of the new cross-community assembly, to be followed quickly by the first IRA weapons surrender. If the IRA did not start "decommissioning"--that is, disarming--within eight weeks, the assembly would be shut down.

Whatever the current proposal is, Trimble reported this morning that his party won't accept it. Some pundits here said there was genuine opposition within the Ulster Unionist Party; others suggested that Trimble was using delay as a bargaining tactic, and still has firm control over his party.