By Richard Cowan and Moira Warburton
WASHINGTON (Reuters) -U.S. Senate Republican Leader Mitch McConnell said on Tuesday he was "comfortable" with the framework of a bipartisan gun violence bill unveiled earlier this week and would vote for it if it is not changed substantially, adding momentum to a compromise that could pass the Senate as early as next week.
"The heavy lifting is done," Senator Chris Murphy, the lead Democrat on the bill, told reporters.
Republican Senator John Cornyn, the lead Republican in the effort, said negotiators could finish writing the bill by the end of this week, clearing the way for a possible vote next week.
McConnell's support is a significant boost to a growing group of bipartisan lawmakers who are expected to back the finished legislation. The bill needs 60 votes to advance in the evenly-split 100-seat chamber, including 10 Republicans.
Crafted in the aftermath of last month's massacres at an elementary school in Uvalde, Texas and a supermarket in Buffalo, New York, the framework is far less ambitious than proposals offered by President Joe Biden and other Democrats.
The plan, lauded by Biden, includes support for state "red flag" laws keeping firearms from potentially dangerous people, tougher criminal background checks for gun buyers under age 21 and a crackdown on "straw purchases" by people buying weapons for others who could not pass a background check.
Senate Democratic Leader Chuck Schumer repeatedly has said he would work quickly to pass the bill once it is written. But thorny issues still need to be resolved.
Cornyn said negotiations were focused on the "red flag" provision.
The legislation would provide money to help other states set up their own laws, but it would not create a national red-flag program, he said. Sixteen states already have red flag laws in place, he said.
The provision should be broadened, he said, so that new federal funding could be targeted at various state programs, such as outpatient treatment programs for people suffering from mental illness.
McConnell said support for the package's provisions was "off the charts" among current gun owners, according to a poll presented to Republican senators.
Ten Republicans, nine Democrats and one independent have joined forces in the Senate on what Democrats are calling a "first step" toward tackling mass murders, such as the recent ones in New York and Texas. In those shootings, semi-automatic weapons were used to kill 10 Black people in Buffalo and 19 elementary school children and two teachers in Uvalde.
Biden and other Democrats pushed to renew an assault weapons ban that expired in 2004. Senate Republicans made it clear this provision and one to raise the age for buying such weapons to 21 from 18 did not have enough support to pass.