Prosecutors are claiming that a serial arson case in Sacramento federal court has national security implications and, in a highly unusual ruling, a judge is allowing the government to withhold parts of the evidence from defense lawyers. Attorneys on both sides declined Monday to comment publicly, but court papers they have filed outline a dispute over the legality of hiding evidence with no obligation to disclose the reasons to the defense team. The case involves three men charged in February in a 60-count grand jury indictment with plotting to commit multiple arsons for profit between 2009 and 2013.