x �David Ignatius, The Washington Post ISTANBUL</p>As the decisive battle for Damascus approaches, the array of Syrian opposition forces facing President Bashar al-Assad appears to share one common trait: Most of the major rebel groups have strong Islamic roots and backing from Muslim neighbors The Free Syrian Army has developed a rough “order of battle” that describes these rebel groups, their ideology and sources of funding. This report was shared last week with the State Department. It offers a window on a war that, absent some diplomatic miracle, is grinding toward a bloody and chaotic endgame. The disorganized, Muslim-dominated opposition prompts several conclusions: First, the United States will have limited influence, even if it steps up covert involvement over the next few months. Second, the post-Assad situation may be as chaotic and dangerous as the civil war itself. The Muslim rebel groups will try to claim control of Assad’s powerful arsenal, including chemical weapons, posing new dangers. Although the Syrian revolution is two years old, the rebel forces still haven’t formed a unified command. Gen. Salim Idriss, commander of the Free Syrian Army, has tried to coordinate the fighters. But this remains a bottom-up rebellion, with towns and regions forming battalions that have merged into larger coalitions. These coalitions have tens of thousands of fighters. But they lack anything approaching the discipline of a normal army. Even though the rebels have only loose coordination, they have become a potent force. They have seized control of most of Aleppo and northern Syria, and they are tightening their grip on Damascus, controlling many of the access routes east and south of the city, according to rebel sources. Free Syrian Army leaders believe that the battle for Damascus will reach its climax in the next two to three months. Rebel shells have hit landmarks in central Damascus, such as the Sheraton Hotel and the neighborhood of Abou Roumaneh, where many diplomats are based. To the east, the rebels now appear to control East Goutha, which commands eastern access to the city, and are firing on the Damascus airport. To the west, they are reportedly shelling the neighborhood of Mezzeh. The lineup of opposition military groups is confusing to outsiders, but rebel sources say there are several major factions. The biggest umbrella group is called the Jabhat al-Tahrir al-Souriya al-Islamiya. It has about 37,000 fighters, drawn from four main subgroups based in different parts of the country. These Saudi-backed groups are not hard-core Islamists but are more militant than the political coalition headed by Sheik Moaz al-Khatib, who last week claimed Syria’s seat in the Arab League. The second-largest rebel coalition is more extreme and is dominated by hard-core Salafist Muslims. Its official name — Jabhat al-Islamiya al-Tahrir al-Souriya — is almost identical to that of the Saudi-backed group. Rebel sources count 11 different brigades from around the country that have merged to form this second coalition. Financing comes from wealthy Saudi, Kuwaiti and other Gulf Arab individuals. Rebel sources estimate about 13,000 Salafist fighters are gathered under this second umbrella. A third rebel group, known as Ahfad al-Rasoul, is funded by Qatar. It has perhaps 15,000 fighters. The most dangerous group in the mix is the Jabhat al-Nusra, which is an offshoot of al-Qaeda in Iraq. By one rebel estimate, it has grown to include perhaps 6,000 fighters. But this group, perhaps fearing that it will be targeted by Western counterterrorism forces, is said to be keeping its head down — and perhaps commingling with the Salafist umbrella group. Idriss and his Free Syrian Army command about 50,000 more fighters, rebel sources say. Realistically, the best hope for U.S. policy is to press the Saudi-backed coalition and its 37,000 fighters, to work under the command of Idriss and the Free Syrian Army. That would bring a measure of order and would open the way for Idriss to negotiate a military transition government that would include reconcilable elements of Assad’s army. “Consolidating forces under Gen. Idriss would extend his recognition and credibility,” explained a Syrian rebel activist here Tuesday night. But without a strong Saudi push, this coordination is a long shot. Rebel sources here say the opposition has developed plans to train Syrian police, purify water supplies and teach forces how to dispose of chemical weapons — all pending approval. Such plans offer the best chance for mitigating the Syrian disaster. What is the United States waiting for?