"Sistani has reservations, but it will not constitute an obstacle," said Mohammed Hussein Bahr al-Ulloum, who helped coordinate talks between some Shiite Governing Council members and the Grand Ayatollah Ali al-Husseini al-Sistani.
"It will be signed as it was agreed upon before the governing council members," he said.
The top U.S. administrator in Iraq, L. Paul Bremer, said in a broadcast interview that he is hopeful but uncertain that the charter will be signed Monday.
In central Baghdad, at least 10 rockets detonated Sunday night near an area that houses the headquarters of the U.S.-led coalition. Sirens blared for several minutes, and smoke and flames were briefly visible.
The former Ministry of Foreign Affairs was on fire, a witness said. The building was severely damaged by U.S. bombing during the war last year. A U.S. military mess hall sits behind the building.
There was no immediate word on casualties.
The rockets struck on the northern edge of the Green Zone, which houses the coalition headquarters. The interim constitution is to be signed
On Saturday, U.S. soldiers opened fire on a truck packed with explosives, killing the driver, and three Americans were wounded when the truck crashed on a bridge and exploded.
In Washington, American officials said a team of 50 Justice Department prosecutors, investigators and support staff will go to Iraq to assemble war crimes cases against Saddam Hussein and others in his former regime.
The officials will sift through thousands of pages of evidence and provide a roadmap for Iraqis to use when they bring Saddam and others regime officials before war crimes tribunals. U.S. officials want the world to view the trials as an Iraqi process, not one run by Americans or other foreigners.
The Governing Council has set up tribunals — three panels of five judges each, with nine other judges serving on an appeals panel — but a timetable for a trial remains unclear.
The potential charges against Saddam, who was captured by U.S. forces on Dec. 14, also remain unclear.
"Trying Saddam Hussein according to international legal rules and bringing him to justice will be difficult at best," says international law professor and CBS News Foreign Affairs Analyst Pamela Falk, "but most important is that the tribunal be Iraqi, not perceived to be victor's justice by the U.S., and will need the experience of war crimes experts who have been involved in similar tribunals to avoid the pitfall of giving Hussein an international platform."
Saturday's apparent vehicle-bomb attack came in Habaniyah, west of Baghdad.
In Amarah, seven British soldiers were wounded in a three-hour firefight with unknown attackers in southern Iraq, coalition officials said. Three Iraqis were killed, British officials said.
On Sunday, Shiite members of Iraq's Governing Council started a second day of meetings in Najaf with Grand Ayatollah Ali al-Husseini al-Sistani, spiritual leader of most of the country's majority Shiites. Details were not immediately available.
Al-Sistani rejected two clauses in the interim charter — one that would have given Iraq's Kurds the power to scuttle a permanent charter and another that would have provided for a single president instead of a rotating leadership.
Reflecting al-Sistani's objections, the Shiite council members refused on Friday to sign the interim constitution hours before it was supposed to be signed, embarrassing U.S. officials and providing a stark reminder of the ayatollah's enormous influence in Iraqi politics.
With negotiations reopened, a Kurdish official said his side would not consent to changing the clause, which was agreed to by the entire council when it approved the constitution on Monday after several days of intense debate.
"We are sticking to it because it's a legitimate demand," said Kosrat Rasul, an official in the Patriotic Union of Kurdistan, one of two main Kurdish parties on the council.
Officials would not comment on the talks among the Shiites in Najaf, and it was not clear whether the Shiite politicians were trying to work out alternatives with al-Sistani, explore what phrasing would be acceptable for him or persuade him to drop his objections.
Still, they said they expected to resolve the dispute by Monday.
"We have announced that Monday is the date for the signing of the law and we are determined to stick to this date," Mohammad Bahr al-Ulloum told reporters in Najaf, site of Shiites' holiest shrine.
The interim constitution, which will remain in effect until the end of 2005 after a permanent charter is approved, is a crucial part of a U.S. plan for handing over power to the Iraqis on June 30. It took intense negotiations last weekend, shepherded by the Americans, to overcome sharp divisions and reach a deal.
Al-Sistani's son, Mohammed, shuttled back and forth between his father's home and Bahr al-Ulloum's office in Najaf, where the Shiite council members gathered Saturday.
Whatever compromise is worked out with al-Sistani must be agreed to by the other 20 members of the council.
"They should have discussed this issue since the beginning. It was a surprise for everyone," Rasul, of the PUK, told AP. "Everybody was prepared to sign the constitution" on Friday.
Mahmoud Othman, an independent Kurd on the council, said he was hopeful the document would be signed Monday. He invited al-Sistani to send a delegate to talks in Baghdad to ensure a deal is reached.
"If Sistani wants to a send a representative to the council, he can," he told Associated Press Television News on Saturday.
Al-Sistani has twice before derailed U.S. plans, with objections to the timetable and methods for transferring sovereignty to an Iraqi government. The Bush administration wants to carry out the transfer well before November U.S. presidential elections.
The Shiites opposed a clause that Kurds got into the charter concerning a referendum planned for next year to approve the permanent constitution. The clause says that even if a majority of Iraqis support the permanent constitution, the referendum would fail if two-thirds of the voters in three provinces reject it.
The Kurds control three provinces in the north, allowing them to stop any constitution that encroaches on their self-rule. Al-Sistani objected to a minority having the power to block any charter approved by the Shiite majority.
Several officials said another cause of dispute was the makeup of the presidency. The draft approved earlier in the week set up a single president with two deputies.
The Shiites revived their demand for a presidency that would rotate among three Shiites, a Kurd and a Sunni — giving the Shiites a dominant role. U.S. and some Iraqi officials, however, said the shape of the presidency was not in dispute.