Because of the opposition the ban has prompted, its exclusion from the initial package the Senate considers had been expected as a way for Democrats to amass the strongest possible vote for the overall legislation. Having a separate vote on assault weapons might free moderate Democratic senators facing re-election in Republican-leaning states next year to vote against the assault weapons measure, but then support the remaining overall package of gun curbs.
Gun-control supporters also consider a strong Senate vote on an overall bill important because it could put pressure on the Republican-run House, whose leaders have shown little enthusiasm for most of Obama's proposals.
Foes of Feinstein's proposal call it a gun grab to take firearms from law-abiding citizens with minimal impact on gun violence. Feinstein and other supporters say limits are needed on the firepower available to people who might make attacks such as the Newtown shootings, which police say involved an assault-type weapon.
Mark Barden, whose 7-year-old son Daniel was killed at Sandy Hook Elementary School, said he hoped an assault weapons ban would pass eventually.
"We're still very happy with the progress that's been made," he said. "Hopefully what is stripped away will return as an amendment."
Two new state laws to limit ammunition magazines and expand required background checks are to be signed Wednesday by Democratic Gov. John Hickenlooper in Colorado, site of another mass shooting last year at a movie theater in Aurora.
Gun-control advocates expressed little surprise over the decision to keep assault weapons out of the initial federal bill.
"If their view is that the assault weapons ban is tougher sledding, we respect that," said Mark Glaze, director of Mayors Against Illegal Guns, which represents hundreds of U.S. mayors seeking gun curbs. He said his group wants Reid's bill to be focused on expanding required background checks for gun buyers, a provision that he called "the biggest policy fix" that could be made.