WASHINGTON, July 2 (Reuters) - A bipartisan group of U.S. lawmakers expert in antitrust urged the Federal Trade Commission Friday to press on with its lawsuit against Facebook Inc (FB.O), according to a statement from Senator Amy Klobuchar. In a letter to new FTC Chair Lina Khan, Klobuchar, Senator Mike Lee and Representatives David Cicilline and Ken Buck urged the FTC to "pursue enforcement action against Facebook and to consider all available options under the law for ensuring that the commission’s claims receive a full and fair hearing." Klobuchar and Cicilline, both Democrats, and Lee and Buck, both Republicans, hold the top positions on congressional antitrust panels. The FTC is expected to file a new complaint against Facebook after U.S. District Judge James Boasberg of District of Columbia dismissed one filed in December, experts said. That complaint, which asked him to require Facebook to sell photo sharing app Instagram and messaging app WhatsApp, fell short, Boasberg said, because the FTC failed to show the company had monopoly power and instances of alleged anticompetitive behavior were too old. read more Several veteran FTC officials said it was implausible that the agency did not have data to back up its assertion that Facebook had "in excess of 60%" of the social media market. "What he told them was "I"m not going to read the newspaper and believe that Facebook is a monopoly"," said Andy Gavil, an FTC veteran who teaches at the Howard University School of Law. Facebook declined to comment for this story. In earlier comment, it noted that Instagram and WhatsApp grew mightily under Facebook stewardship. It said it would vigorously fight the FTC in court. GO BIG AND GO HOME? The FTC, under new leadership, might write a considerably broader complaint and could file it before an FTC administrative law judge, essentially taking the case in-house. William Kovacic, a former FTC chair now at George Washington University Law School, said that a new complaint could add allegations, including potentially unfair method of competition. "That is a topic that she (Khan) has talked about and written about on many occasions," he said. Experts also predicted the dismissal would build support for bills to ramp up antitrust enforcement. read more "If these dismissals tip the scales, it will be toward doing something. If the government could win even modestly on these cases, it"s an argument to do nothing," said Herb Hovenkamp of the University of Pennsylvania Carey Law School.