The city of South Portland has asked a federal judge to dismiss a lawsuit by the Portland Pipe Line Corp., saying that the company has no case because it has “no current plans” to reverse the flow of the pipeline to bring Canadian crude oil to Portland Harbor. The city is defending its Clear Skies ordinance, approved last summer, which bans loading crude oil into tankers in the harbor and effectively prevents the company from reversing the flow of its South Portland-to-Montreal pipeline to brings Canadian tar sands oil into Maine. The city’s lawyers contend that the company has jumped the gun in claiming the ordinance violates constitutional rights, federal statutes and maritime laws, noting that the company’s concern is to maintain the future ability to “respond to market conditions,” according to a motion filed Tuesday in U.S.