WASHINGTON — The new TV ratings program guidelines may provide a shield for broadcasters to pro-vide even more primetime bathroom humor, said Senate Communications Subcommittee chairman Conrad Burns (R-Mont.) Tuesday.The ratings system may be an excuse “to walk out on responsibility,” Burns said. He made the comments after a speech to the Media Institute, a Washington-based First Amendment think tank. Burns is the second influential Senate Republican to criticize the program labeling system implemented by the television industry on Jan. 1. Senate Commerce Committee chairman John McCain (R-Ariz.) has also knocked the ratings system, saying it does not provide enough information to parents. McCain plans to hold a hearing on the ratings guidelines next month. Burns also called on the liquor industry to come up with voluntary guidelines for advertising on television. He suggested that neither the Federal Communications Commission nor the Federal Trade Commission should get involved in the issue. The FTC is already investigating the advertising practices of Stroh Brewing and Joseph Seagram Ltd. Although FCC chairman Reed Hundt has expressed an interest in the issue, he has had trouble getting his fellow commissioners to support an inquiry.