FIREARMS LIMITS GAINING SUPPORT IN LEGISLATURES
Many state legislatures, spurred by Littleton, Colo, school shooting, are approving gun-control laws, in some cases taking up measures that had long been considered unlikely to pass; gun-rights proponents, under pressure since Apr 20 shooting, are pulling back their bills; Colorado lawmakers have abandoned push for new laws to expand right to carry concealed weapons and to bar local governments from passing gun-control laws (M)