Anxious House Braces for Fight On Gun Control
House members return from weeklong recess and prepare for battle over gun control that is even more fraught with political anxiety than it had been when they left; increased tensions over new gun-control measures partly reflect activity of National Rifle Association, which used Congressional recess to rally its supporters, lobby lawmakers and sprinkel radio airwaves with advertisements opposing measures; House battle will provide definitive measure of rifle association's political muscle in aftermath of series of fatal school shootings that created momentum for more restrictions on firearms; NRA is pursuing much more aggressive campaign in House than it was able to organize in Senate (M)