Hollywood exex are expected to face a grilling today at a Senate hearing on TV violence.Issue of TV violence has suddenly become all the rage on Capitol Hill, with lawmakers threatening retribution if the industry doesn’t curb excessive gore in programming. One lawmaker — House telecommunications subcommittee chairman Ed Markey (D-Mass.) — is urging the industry to adopt an MPAA-like rating system to warn parents of violent shows. Today’s hearing will be chaired by Sen. Paul Simon (D-Ill.), who sponsored 1990 legislation that gave the Big Three networks a three-year exemption from antitrust laws to develop anti-violence guidelines. Witnesses skedded to testify include Motion Picture Assn. of America prez Jack Valenti; Kerry McCluggage, head of Paramount Pictures’ Television Group; King World Prods. chief operating officer Stephen Palley; Lorimar Television prez Leslie Moonves; and Al DeVaney, chairman of the board of the Assn. of Independent Television Stations. Also appearing will be Dr. Leonard Eron of U. of Michigan’s Institute for Social Research and Dr. William Dietz of the American Academy of Pediatrics.