By Mariam Karouny BAGHDAD, Jan 15 (Reuters) - A major U.S.-backed operation to curb militia violence in Baghdad will take at least six months and is probably the final chance for the increasingly shaky government, senior Iraqi political sources said. Operations were expected to begin next week and last for as long as seven months, one source said. Prime Minister Nuri al-Maliki and U.S. President George W. Bush have announced plans to reinforce the capital with thousands of Iraqi and U.S. troops to smother the sectarian violence that is pitching Iraq towards all-out civil war. The top U.S. general in Iraq said on Monday some had already arrived. Bush has said the operation will "in large part determine the outcome in Iraq" and senior Iraqi officials from the Shi'ite Islamist majority dominating the government said they believed it was a "last chance" that must be implemented thoroughly. "The key element of this plan will be the time. The troops will take their time, actually all the time they need to clean an area," one senior politician said late on Sunday. "The plan will last at least for six months." A previous attempt to clear militants district by district failed last summer because U.S. commanders said there were not enough Iraqi troops to hold gains made by the Americans and because Shi'ite politicians stopped them arresting or killing leading Shi'ite militants. "The final touches are being put out now on the plan," another senior politician told Reuters, forecasting a start next week. U.S. General George Casey warned on Monday not to expect instant results, saying he foresaw a "gradual evolution" over two to three months and then better security by the summer. The political sources said that there were only some logistics to finalise, such as bringing additional troops into Baghdad. Officials wanted to ensure the broadest possible political support for the operation, including from radical Shi'ite leaders such as young cleric Moqtada al-Sadr. Government leaders had also been visiting the top Shi'ite cleric, Grand Ayatollah Ali al-Sistani, to ensure his backing. "LAST CHANCE" U.S. commanders and Iraq's once dominant Sunni minority have made clear they want any crackdown to include not just Sunni rebels but militias loyal to powerful Shi'ite Islamists, notably Sadr's Mehdi Army, which they blame for death squad killings. Shi'ite officials said Sadr supported the plan. "This is the last chance. The Americans will give up on us after the seven months," one senior Iraqi official said. "If this plan fails other options will be weighed, among them the United Nations coming in to run Iraq with a government of national salvation," he added. The Shi'ites, including Sistani, are worried about what will happen next if this plan fails. In some of their strongest comments yet, they bore out remarks from Bush and other U.S. officials that Maliki, a compromise prime minister who owed his appointment to support from Sadr, is now ready to deal militarily with Shi'ite militias. Another senior Shi'ite official said: "We now have a 60 percent chance of failure. This plan is our only hope. We as Shi'ites have no choice but to stand behind Maliki and strike hard at whoever wants to spoil our achievements. "Those militias have no other choice but to give up ... We will not accept any more games ... The militias will be hit even if they hide in mosques." Maliki has said the plan will target militants regardless of their religion, but Bush's domestic opponents, sceptical of his decision to send 21,500 more troops to Iraq, question whether they can trust Maliki to keep his word. U.S. commanders say it is crucial to the Baghdad plan's success that the Shi'ite-led government take on fellow Shi'ites as well as insurgents from Saddam Hussein's Sunni Arab minority. Washington has identified Sadr's Mehdi Army as the greatest threat to security in Iraq. General Casey, the most senior U.S. officer in Iraq, said on Monday Maliki had pledged there would be no constraints or political interference and operations would take place in all districts of the city, regardless of sect. "The prime minister is quite clear ... that militias will not be allowed to be an alternative to the state," Casey said. U.S. Ambassador Zalmay Khalilzad said at a news conference with Casey he was confident Iraqi leaders understood the gravity of the situation, which he called a "defining moment" for Iraq. Khalilzad said the Iraqi people would decide Maliki's fate if he fails: "Iraq is a sovereign country." (Additional reporting by Claudia Parsons)
