Sen. Dianne Feinstein (D-Calif.) stands next to a display of assault weapons during a January news conference on Capitol Hill. (Alex Wong/Getty Images)

Senate Democrats are preparing to move ahead with consideration of several proposals to limit gun violence, but prospects for the controversial ban on hundreds of specific weapons and parts are diminishing, according to lawmakers and aides familiar with the process.

Sen. Dianne Feinstein (D-Calif.), the chief sponsor of the ban, said Tuesday that her proposal won't be included as part of a bill encompassing several proposals that the Senate Judiciary Committee approved last week and that the Senate is expected to begin debating when it returns from a two-week recess in early April.

In addition to the assault weapons ban, the Judiciary Committee approved a bipartisan proposal to make gun trafficking a federal crime; a bipartisan bill to expand a Justice Department grant program that provides funding for school security; and a Democratic proposal to expand the nation's gun background check program.

Instead of including the assault weapons ban in the final bill, Feinstein said Senate Majority Leader Harry M. Reid (D-Nev.) has told her she can introduce it as an amendment to the full bill -- fulfilling his promise to hold an up-or-down vote on the measure. A separate vote will be held on an amendment to limit the size of ammunition clips, she said.

Reid said later Tuesday, however, that the amendment has no chance of passing. "Right now her amendment, using the most optimistic numbers, has less than 40 votes. I -- that's not 60," Reid said. "I have to get something on the floor so we can have votes on that issue and the other issues that I've talked about. And that's what I'm going to try to do.”

"Obviously I was disappointed" when she heard the news, Feinstein told reporters Tuesday.

"The enemies on this are very powerful, I've known that all my life," Feinstein added, referring to the National Rifle Association. "But I'm confident this bill would be constitutional."

Reid's decision is a setback for President Obama and congressional Democrats, who are pushing a series of proposals to limit gun violence in the wake of the Sandy Hook Elementary School shooting in Newtown, Conn.

The most ambitious and controversial proposal backed by the White House, Feinstein's bill would ban almost 160 specific semiautomatic weapons and rifles and assorted military-style parts and also limits the size of ammunition clips to 10 rounds, banning larger rounds used in some of the more recent and brazen mass shootings. The ban has 22 other Senate Democratic co-sponsors, including Feinstein.

A bill limiting the size of ammunition clips was originally introduced by Sen. Frank Lautenberg (D-N.J.), but was merged with Feinstein's bill and approved by the Judiciary panel.

Sen. Richard Blumenthal (D-Conn.), who along with Feinstein has led the charge for an assault weapons ban, said he remained hopeful that the bill could succeed.

"I think we have growing momentum on our side," Blumenthal said. "Newtown was a call to action and I think we've made tremendous progress. Three-plus months ago, this issue was politically untouchable. This time is different."

Over the Easter recess, Blumenthal said he expected advocates for the ban to continue meeting with lawmakers in their home states. "They have been very compelling when I've seen them talk to my colleagues," he said. "I've had families visit Washington and talk to a number of my colleagues privately. It's been very, very powerful."

Senior Senate Democratic aides called talk of the ban's demise "premature," but admitted that it is unlikely to be included as part of the broader package, which could be introduced by Reid as early as this week.

Still unresolved is what Reid's final bill might say about expanding the gun background check program. Sen. Charles E. Schumer (D-N.Y.) is working with other Democrats to find potential Republican co-sponsors for a revised bill that would permit exceptions for firearm exchanges between family members or close friends. But talks have been hampered by disagreements over whether to establish a record-keeping system for non-commercial gun transactions.

"Hopefully reasonable people will look at reasonable proposals and something will happen," said one of the negotiators, Sen. Joe Manchin III (D-W. Va.).

Follow Ed O'Keefe on Twitter: @edatpost

This post has been updated.

Note: An earlier version of this story said the assault weapons ban would not be included in the bill. While its inclusion is unlikely, no final decision has been made. The story has been updated.