ZAWIYA, Libya — Libyan rebels and troops loyal to Moammar Gadhafi fought for control of Zawiya on Sunday, a day after opposition forces pushed from the western mountains into the strategic city in their most dramatic advance in months. The city of 200,000 just 30 miles (50 kilometers) west of Tripoli attempted to rise against Gadhafi months ago, near the start of Libya’s civil war, but was crushed.