Wednesday's vote was a jarring blow to the drive to curb firearms sparked by December's massacre of children and staff at an elementary school in Newtown, Conn. President Barack Obama made broadened background checks the centerpiece of his gun control proposals.
The roll call was also a victory for the National Rifle Association, which opposed the plan as an ineffective infringement on gun rights.
The proposal would have required background checks for all transactions at gun shows and online. Currently they must occur for sales handled by licensed gun dealers.
The system is designed to keep criminals and people with mental problems from getting guns.