WASHINGTON -- A key vote to allow debate on a package of gun-related measures proposed in response to the Newtown school shootings will be held Thursday, with Democratic leaders increasingly confident they'll get the support of enough Republicans to win.

Senate Majority Leader Harry Reid (D-Nev.) scheduled a vote to break a filibuster by 14 Republicans who want to block the Senate from taking up the package, as senators appeared to be close to reaching a crucial bipartisan compromise on gun sale background checks.

Reid said he was unsure he had the necessary 60 votes to start debate. But the Democratic Policy and Communications Committee chaired by Sen. Charles Schumer (D-N.Y.) circulated an email listing at least nine Republicans who have said or indicated they'll vote against the filibuster.

"We're moving forward on this bill. The American people deserve a vote on this legislation," said Reid, as the White House continued to press Congress to act on the gun package.

That pressure included visits to lawmakers by 11 families of victims in the Newtown, Conn., shootings, in which 20 children and six adults were gunned down. The families flew Monday to Washington with President Barack Obama.

In a key development, Sen. Joe Manchin (D-W.Va.) and Sen. Pat Toomey (R-Pa.) -- both with top NRA ratings -- were negotiating a compromise on background checks that could make it easier for the gun package to pass. Manchin and Toomey were still negotiating but getting close, a Toomey spokeswoman said.

"We're not there yet, but we're closer than we've ever been," said Schumer as he left a meeting in Reid's office.

Reid said earlier, "I'm going forward on this regardless of whether it's a compromise or not."

If the filibuster is broken, the Senate is expected to spend at least next week debating and voting on amendments to the gun legislation.

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But prospects for final passage are clouded by wavering Democrats in conservative states who face re-election next year.

The package Reid said he would bring to the floor was approved in the Senate Judiciary Committee and includes universal background checks, a ban on straw purchases and gun trafficking, and funding for school safety. The heart of the package is the background check measure sponsored by Schumer, which has broad public support in polls.

The NRA and conservative senators including Rand Paul of Kentucky and Ted Cruz of Texas say it infringes on Second Amendment rights and could lead to a gun registry.

Senate Minority Leader Mitch McConnell (R-Ky.) said he backed the filibuster because the committee approved the bills without bipartisan support.

Reid said that if the filibuster is broken, he would allow amendments to the bill -- "let the cards fall where they may" -- including banning assault weapons and limiting the size of ammunition magazines.