The federal government is considering a proposal to allow visitors to carry loaded, concealed weapons in some national parks, wildlife refuges and monuments. The National Rifle Association favors the proposed rule, arguing that it would help keep crime down and protect visitors from potentially dangerous wildlife. "You read stories about people attacked by animals or who stumble upon meth labs or women who are raped in a national park,' the N.R.A.'s chief lobbyist, Chris W. Cox, said. "We don't believe law-abiding citizens should be kept from protecting themselves and their families in national wildlife refuges or in national parks.' But opponents, including several former National Park Service officials, say that the current rules are effective