The action sent a strong signal that the measure, which has bipartisan support but is opposed by many police chiefs and mayors, is destined to pass.
By a 75-22 vote, lawmakers agreed to begin debating the bill, which would protect firearms manufacturers and dealers as long as they did not sell defective weapons or violate any law. The question is whether the Senate will tack two gun-control measures onto the bill.
Those measures - one to extend the so-called assault-weapons ban, and another to require instant background checks for gun show customers - also have bipartisan support and are backed by President Bush. But in a blow to the senators pushing the measures, the White House announced late Tuesday that it opposed attaching them as amendments.
"For the president to say he's for the assault-weapons ban, but to act against it, is a flip-flop if there ever was one," Democratic Sen. Charles E. Schumer of New York told reporters yesterday afternoon.
Schumer's remarks, a reference to Bush's recent criticisms of Sen. John Kerry of Massachusetts, a Democratic presidential primary contender, illustrate the political volatility of the gun issue, which is expected to dominate Senate debate for at least the rest of this week.