Politicians were still being briefed on the agreement last night, and no official announcement had been made. If it holds, the deal would offer another example of what has become politics as usual in Iraq: A mounting crisis threatens to cast the country into further ethnic and sectarian strife, before a closed-door solution is reached at what appears to be the last minute.

While security has improved markedly in the last year, the latest political crisis had led to Sunni Arab and even Kurdish calls for a boycott of the election. The Sunni threats were reminiscent of 2005, when the community largely stayed away from voting - a decision many see as having set the stage for brutal internecine strife in 2006 and 2007.

"We've reached an understanding," said Abdul-Ilah Kazem, a spokesman for Vice President Tariq al-Hashimi, a Sunni Arab and key player in the crisis.

Even with the agreement, which must now be approved by the Iraqi electoral commission, election officials said it would be almost impossible to hold the election in January as originally planned. Middle to late February was more likely, since a major Shiite Muslim holiday will not end until Feb. 10.

The elections law was originally passed Nov. 8, in a vote hailed by the Obama administration, which sees the election as a milestone in its plans to withdraw all but 50,000 troops from the country by August. But Hashimi, one of three members of Iraq's Presidency Council, each with the power of veto, rejected the law, saying it gave too little representation to millions of Iraqi exiles, many of them Sunni Arabs.

Parliament amended the law this week, with a change that appeared to backfire on Hashimi. Under the revision, Iraqi exiles would be counted in their home provinces. But a new way of allotting seats meant that majority Sunni provinces would have fewer members of parliament than they would have had under the original law.

Sunnis were outraged, although some blamed Hashimi for rejecting a deal that became worse the second time around. Hashimi himself was angry, and hours after the vote, his aides and supporters said he would almost certainly veto it.

Under the tentative new agreement, brokered in part by Hadi al-Ameri, a Shiite Islamist lawmaker, the law would be read as liberally as possible, so that the original number of seats could be restored to Nineveh, a majority Sunni province and a fault line between Arabs and Kurds in northern Iraq, said lawmakers and political aides. The number of seats in other provinces would remain the same, they said.