Centerpiece of Gun Bill Remains in Doubt

The Senate could vote as early as Tuesday on expanded background checks for gun buyers â€" a centerpiece of broad gun legislation â€" but leading lawmakers said Sunday that approval of the measure remained uncertain.

“I think it’s an open question as to whether or not we have the votes,” Senator Patrick Toomey, Republican of Pennsylvania, said on the CNN program “State of the Union.” Mr. Toomey is a co-author of the background-check measure. “I think it’s going to be close,” he said.

The other author of that measure, Senator Joe Manchin, Democrat of West Virginia, said he felt that the 60 votes needed to pass the bill would turn up once his colleagues read it.

“We’re asking people to read it,” Mr. Manchin said on CNN. He said that if gun-rights groups like the National Rifle Association will not support the bill, “we just agree to disagree. But there’s things in this piece of legislation that they’ve been working for many, many years to get, and it’s here.”

The two lawmakers, both gun owners, did get a boost from Senator John McCain, Republican of Arizona, who indicated support for their measure, which would close loopholes for gun buyers who have been able to avoid them in many cases at gun shows and through Internet sales.

“I’m very favorably disposed,” Mr. McCain said, adding: “Eighty percent of the American people want to see a better background check procedure.”

The amendment offered by Senators Toomey and Manchin is set to replace the background check provision in legislation about to hit the Senate floor, after the chamber voted 68-31 last Thursday to open debate on the legislation. It would be the first amendment to the bill, which also has provisions to create harsher penalties for the so-called straw purchasing of guns, in which people buy guns for others who are not eligible.

Subsequent amendments, dealing with mental health, a ban on assault weapons and other issues, are expected in the days ahead before a vote on the overall legislation, which could take weeks.

At least one Democrat remained hopeful on Sunday. Senator Kirsten Gillibrand of New York, who was involved in crafting the components of the bill that would address gun trafficking and straw purchasing, said on the NBC program “Meet the Press” that the overall legislation represented a good compromise between pro gun-rights and pro gun control lawmakers.

“This bill will work,” she said, “and this compromise will work. Because it is making sure that you protect second amendment rights while not undermining second amendment rights by saying, criminals have to go through a background check before they can buy that weapon.”