In addition to banning the manufacture, sale, transfer or importation of semi-automatic rifles and pistols that can accept detachable magazines and have at least one military feature, the legislation -- titled "The Assault Weapons Ban of 2013" -- would ban magazines holding more than 10 rounds of ammunition and place new security requirements on people who already own such weapons, The Hill reported.
It would also apply to semi-automatic rifles and handguns with fixed magazines capable of carrying more than 10 rounds, and all semi-automatic shotguns with folding or detachable stocks, pistol grips, forward grips or fixed magazines with room for more than five rounds, The Hill said.
It exempts assault weapons that are "lawfully possessed" as of the date the bill is enacted, but sales of exempted weapons would be subject to background checks.
"No weapon is taken from anyone," Feinstein said. "The purpose is to dry up the supply of these weapons over time."
Feinstein said getting the bill through Congress will be "an uphill battle," but she said it would be "a battle worth having."
"We must balance the desire of a few to own military-style assault weapons with the growing threat to lives across America," she said.
New York Gov. Andrew Cuomo last week signed into law a state ban similar to Feinstein's proposed measure.
National Rifle Association President David Keene said Wednesday New York's ban on assault weapons was likely unconstitutional and his organization planned to file a "notice of claim" against the state -- the first step toward a possible lawsuit.
"A so-called assault-weapons ban in today's world is probably unconstitutional," Keene told radio station WGDJ, Rensselaer, N.Y., citing the U.S. Supreme Court's 2008 ruling in District of Columbia vs. Heller, which he said prevents the government from banning "commonly used firearms."
Associate Justice Antonin Scalia's opinion for the majority provided Second Amendment protection for commonly used and popular handguns, but not for atypical arms or arms used for unlawful purposes, such as sawed-off shotguns.
White House spokesman Jay Carney told reporters Thursday it will be difficult to win congressional passage for some of President Barack Obama's proposals on gun control but that "doesn't mean that we should not work aggressively to achieve them. There's broad public support for taking action."
Obama has said a top priority is to get "an assault weapons ban that is meaningful" passed this year. Carney noted none of Obama's proposals "would take a gun away from a single, law-abiding American citizen."
The Sandy Hook Elementary School shooting in Newtown, Conn., provided the backdrop for the Feinstein bill as Democratic Sens. Richard Blumenthal and Chris Murphy of Connecticut, as well as Democratic Rep. Elizabeth Esty, whose district includes Newtown, joined Feinstein in introducing the measure.
Twenty students and six staff members at the elementary school were killed in the Dec. 14 attack. Among the weapons Adam Lanza had was an assault rifle.
The U.S. Conference of Mayors, the Major Cities Chiefs Association, the Police Foundation and the International Association of Campus Law Enforcement Administrators have endorsed the bill introduced Thursday, The Hill said.
Blumenthal told Hearst Newspapers the new bill would "be a more stringent measure than the assault weapon ban that existed from 1994 to 2004."
He said the ban on assault weapons and high-capacity magazines would work hand-in-hand with heightened school security and mental-health reform.
"This measure is a significant first step as part of a comprehensive program," he said.
The bill introduced Thursday has no sunset clause, unlike the bill Feinstein wrote -- and Congress passed -- in 1994. It expired in 2004.
Critics of the 1994 ban have said it was ineffective because gun companies simply re-engineered weapons to get around its requirements.