Democrats say they will include expanded background checks for firearms purchasers in the gun-control measure the Senate debates next month.
The announcement by Senate Majority Leader Harry Reid signals that Democrats will press forcefully in their drive to close background check loopholes. Polls show the public overwhelmingly supports the idea.
Reid says the gun measure will also create tougher laws and stiffer sentences for illegal gun trafficking and increase federal grants for school safety.
Requiring background checks for private gun transactions is the centerpiece of President Barack Obama's response to the slaying of first-graders and educators at a school in Newtown, Conn.
Opponents say criminals ignore background checks in getting guns illegally and that the expansion could lead to a federal registry of gun owners.