The continuing strife has widened the divide between the majority Shiite Muslim population, which could gain control of the country through Jan. 30 parliamentary elections, and Sunni Muslims, many of whom are planning to boycott the elections and a minority of whom have turned to violence.
Even should the elections proceed, they now hold little prospect of producing a government that would be broadly acceptable to Iraq's diverse ethnic groups.
While a number of politicians in and out of the interim Iraqi government - including the president, defense minister and ambassador to the United Nations - have said the security climate would make the elections difficult, U.S. officials and Shiite religious leaders are forging ahead.
Interim Prime Minister Iyad Allawi, a secular Shiite who stands to lose in the election if religious clerics prevail, is growing increasingly anxious about the voting, scheduled for Jan. 30.
''Given any excuse, he'd bail,'' a senior administration official in Washington said of Allawi.
Even so, President Bush and his top advisers see no choice but to hold the election on schedule.
The senior official, who spoke only on condition of anonymity because his remarks were not authorized, said any delay now would mean more trouble for the United States because Iraq's Shiite majority and its spiritual leaders insist that the balloting proceed.
Neither U.S. troops nor Iraqi security forces have been able to halt or even slow the widespread murder and intimidation of prospective voters and candidates in Sunni areas, including Baghdad itself, as CIA officers in Iraq reported last month.
If the elections proceed, Sunni involvement probably would be minimal, raising the prospect that the minority Sunni population, which controlled Iraq for most of the past century, would resist the authority of any new government.
The major Sunni party has withdrawn its ticket of candidates. There are neither voter registration centers nor any registered voters in the Sunni strongholds of Fallujah and Ramadi. In several other major Sunni areas - Samarra, parts of the Diyala province and nearly all of Mosul - no voters have registered either.
There have been suggestions of guaranteeing Sunnis a set percentage of seats in the parliament or pushing the elections back to give parties more time to organize.
But to delay the elections would risk the ire of Grand Ayatollah Ali al Husseini al-Sistani, the leading Shiite cleric. While he has not threatened violence, his word could lead to widespread unrest among the Shiite population, thought to make up about 60 percent of Iraq.