As the U.S. Senate prepares to begin debate this week on the biggest gun-control bill in nearly two decades, the gun rights lobby and its Senate allies are working on a series of amendments that have the potential to do the opposite — loosening many of the restrictions that exist in the current law.

Most worrisome to those who advocate new firearms limits is an expected amendment that would achieve one of the National Rifle Association's biggest goals: a "national reciprocity" arrangement, in which a gun owner who receives a permit to carry a concealed weapon in any one state would then be allowed to do that anywhere in the country.

Other progun proposals will make it easier for dealers to sell their merchandise between states or allow certain people who have been treated for mental illness to regain the right to purchase weapons.