After an onslaught of criticism from the networks that its indecency rules were arbitrary and vague, the FCC finally fought back. The lowdown: Networks should steer clear of the seven dirty words in prime time. And the FCC adds in a brief filed in the New York Court of Appeals that even if the commission has allowed uses of cuss words in some instances but not in others, it is free to change its policy. The networks claim that they can’t discern what the FCC policy is, given that the use of the “f—” word on a Fox broadcast of the Billboard Music Awards was declared indecent while a fine against CBS’s “The Early Show” was dropped because the use of the expletive was found to be fleeting. But the FCC says that it has made its explanations of its decisions amply clear. Swearing in a broadcast of “Saving Private Ryan” was OK, but that was a case where the use of profanity has artistic merit. Fox never claimed that the Billboard incident had such merit, the FCC said. The Commission also said that broadcasters have “only limited First Amendment” protection and that the V-chip was “ineffective.”