As San Francisco prepares to ask the Supreme Court to ease federal restrictions on sewage pollution into the ocean and the bay, the case has divided the city’s all-Democratic leadership, and put the city in the unusual position of siding with oil companies and business groups and against the state and federal governments. The Board of Supervisors will take up a resolution Tuesday urging city officials to settle the case and avoid a ruling that could harm offshore water quality nationwide.  San Francisco is siding with “the nation’s biggest polluters” in a lawsuit that “has the potential to seriously destabilize Clean Water Act protections at a time when environmental protections are already under serious threat,” said the resolution by Supervisors Myrna Melgar and Aaron Peskin.