WASHINGTON—Facebook is asking that the new head of the Federal Trade Commission step away from decisions on whether to continue the agency’s antitrust case against the social network giant, asserting that past public criticism of the company’s market power makes it impossible for her to be impartial. Facebook Inc. petitioned the agency Wednesday to remove Chair Lina Khan from taking part in decisions on the FTC’s antitrust lawsuit against the company. A federal judge recently dismissed the suit by the FTC and one from a coalition of states, saying they didn’t provide enough evidence to prove that Facebook is a monopoly in the social networking market. The judge, however, allowed the FTC to revise its complaint and try again. Khan has been a persistent critic of Amazon, Google and Apple, as well as Facebook. FTC officials declined comment on Facebook’s motion, which came two weeks after Amazon requested that Khan …