Supporters of a bipartisan proposal to expand background checks for gun sales are racing to secure Senate votes this week for what would be the most significant gun-control legislation in years.

Opponents, meantime, are raising questions about whether the measure would reduce gun violence or could have prevented the recent high-profile shootings, such as in Newtown, Conn., that motivated lawmakers to act.

Many gun-rights supporters argue that background checks do little to prevent gun violence, saying that firearms can be bought readily on the black market.

Gun-control advocates, while hailing the measure as a move in the right direction, lament a compromise that would exempt private firearm sales from the checks, including to friends and neighbors of gun owners.