BAGHDAD — The top U.S. envoy to Iraq said Monday that the 2003 toppling of Saddam Hussein's regime had opened a "Pandora's box" of volatile ethnic and sectarian tensions that could engulf the region in all-out war if America pulled out of the country too soon.
In remarks that were among the frankest and bleakest public assessments of the Iraq situation by a high-level American official, U.S. Ambassador Zalmay Khalilzad said the "potential is there" for sectarian violence to become full-blown civil war.
For now, Iraq has pulled back from that prospect after the wave of sectarian reprisals that followed the Feb. 22 bombing of a Shiite Muslim shrine in Samarra, he said. But "if another incident [occurs], Iraq is really vulnerable to it at this time, in my judgment," Khalilzad said in an interview with The Times.
Abandoning Iraq in the way the U.S. disengaged from civil wars in Lebanon, Afghanistan and Somalia could have dramatic global repercussions, he said.
"We have opened the Pandora's box and the question is, what is the way forward?" Khalilzad said. "The way forward, in my view, is an effort to build bridges across [Iraq's] communities."
Khalilzad's central message that the United States cannot immediately pull out of Iraq jibed with Bush administration policy. But he offered a far gloomier picture than assessments made in recent days by U.S. military spokesmen.
On Sunday, Marine Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said in a televised interview that things in Iraq were "going very, very well, from everything you look at."
Khalilzad's comments came just before key U.S. decisions are expected on whether the situation in Iraq has improved enough to allow for a reduction in U.S. forces this year.
Army Gens. John P. Abizaid, who heads U.S. Central Command, and George W. Casey, commander of U.S. forces in Iraq, plan to meet with President Bush as early as this week to make recommendations on troop levels.
Military officials must decide this month whether to cancel deployments of several Army combat brigades -- a cancellation that would lead to a reduction in the total number of U.S. troops in Iraq by midyear, from about 130,000 to about 100,000. For nearly a year, Casey has said that a "substantial reduction" in troops could occur in 2006, and cited spring as the time when the critical decisions would be made.
A reduction would signal the administration's confidence in progress in the country. On Friday, however, Casey said that war planners would take the recent violence as "certainly something that we will consider in our decisions."
Without touching on the issue of troop reduction, Khalilzad described a highly combustible atmosphere in Iraq that dates at least to the polarizing Dec. 15 legislative elections, which handed Shiites a dominant role in the government.
"Right now there's a vacuum of authority, and there's a lot of distrust," said the diplomat, who is among the architects of the U.S. plan to reshape the political balance of the Middle East after the Sept. 11 attacks.
The Samarra bombing and the subsequent outbreak of violent reprisals by Shiites against Sunni Muslims demonstrated that insurgents fully understand Iraq's fragility and will seek to exploit it, Khalilzad said.
"It indicates that they recognize this vulnerability of Iraq or this problem in Iraq, which they have tried to fan," he said. "There is a concerted effort to provoke civil war. The guys who want to start a civil war are there looking or considering other things they could do."
Khalilzad, who is actively and publicly involved in Iraq's government talks, repeated his weeks-long assertion that the best way to prevent civil war or large-scale sectarian violence is to form a government drawing from all of Iraq's disparate groups as a way "to build trust and narrow the fault line that exists" between Shiites and Sunnis.
"Once a national unity government is formed, the effort to provoke a civil war will face a huge obstacle," he said.
Shiite leaders loudly objected last week to Khalilzad's involvement in government talks, saying he was improperly taking the side of the Sunni minority.
"I have gotten some negative reaction," Khalilzad said, adding that he had not tried to intervene on the Sunni side. He said he had called for nonsectarian figures to run key ministries. "Sectarian Sunnis are as bad as sectarian Shias," he said.
In any case, Khalilzad said the U.S. has little choice but to maintain a strong presence in Iraq -- or risk a regional conflict in which Arabs side with Sunnis and Iranians back Shiites, in what could be a more encompassing version of the 1980s Iran-Iraq war, which left more than 1 million dead.
The ambassador warned of a calamitous disruption in the production and transport of energy supplies in the Persian Gulf. He described a worst-case scenario in which religious extremists could take over sections of Iraq and begin to expand outward.