Sen. Kay Hagan (D-N.C.), facing reelection this fall, works with her staff in the Senate Reception Room on Tuesday. (Melina Mara/The Washington Post)

Updated and corrected 11:58 a.m.

Fifteen months since gun legislation stalled on Capitol Hill, the Senate is on the verge of a new fight over whether to expand gun rights, an unanticipated development at a moment of already high tension in the fractured chamber.

A new political gun fight would be the first since a bipartisan gun-control measure was swiftly defeated in April 2013, just four months after national outrage over a mass shooting at an elementary school in Newtown, Conn., sparked calls for new legislation. The possibility of a new, mostly partisan debate on gun control likely would upend debate on a bipartisan measure to expand hunting rights on federal lands that is considered a potential political lifeline for about a half dozen Democrats seeking reelection in Republican-leaning states.

Senators of both parties are readying gun-related amendments and are poised to introduce them this week. Republicans want to overturn the ban on large-capacity magazines and assault weapons in the District of Columbia; expand the right to purchase or transport firearms and ammunition across state lines; limit when a military veteran can be denied a firearm due to mental illness; and allow gun owners to carry weapons into post offices or other federal sites. Democrats said they are working on proposals to limit the sale of certain weapons and ammunition; expand the national background-check system; and stiffen penalties for gun straw purchasers.

The proposals would be added to the Bipartisan Sportsmen Act, a measure that would make it easier to hunt and fish on some federal lands, allow the construction of more public shooting ranges at national parks and wildlife refuges and make it easier to purchase federal permits to hunt ducks, geese and other waterfowl. Those and about a dozen other proposals in the bill are popular in rural states where hunting and fishing are common.

Sen. Kay Hagan (D-N.C.), who faces one of the most challenging reelection fights this year, is a lead sponsor of the measure along with Sen. Lisa Murkowski (R-Alaska). The bill has a total of 26 Republican co-sponsors, making it one of the most popular legislative proposals debated by the Senate this year. A similar version of the bill was debated in the Senate in 2012 but failed to advance amid GOP opposition.

Hagan's involvement is notable because she, along with Sens. Mark Begich (D-Alaska), Mary Landrieu (D-La.), Mark Udall (D-Colo.), Jeanne Shaheen (D-N.H.) and Mark Pryor (D-Ark.), have earned special attention from Senate Majority Leader Harry M. Reid (D-Nev.) this year as they run for reelection.

At several points in the past several months, Reid and Democratic leaders have either carved out time for floor debate of bills sponsored by the senators or allowed them to play prominent roles during the debate of other bills designed to become campaign fodder — regardless of whether they ultimately pass Congress.

When the Senate debated making fixes to the national flood insurance program, Landrieu — who represents a state still rebuilding from Hurricane Katrina and other natural disasters — played a prominent role in floor debate even though she wasn't the lead author of the bill. Same for Pryor, who was a major advocate for two veterans' bills that were ultimately defeated. Shaheen and Sen. Rob Portman (R-Ohio) earned floor time to debate long-sought bipartisan fixes to the nation's energy efficiency programs, but the measure was defeated in a dispute with Republicans over amendments.

This week is Hagan's turn, and she touted the bipartisan spirit of her bill Monday night as the Senate agreed to proceed with debate.

"I recognize members on both sides of the aisle have ideas for how to strengthen our bill," she said, adding later: "I encourage my colleagues who have amendments to file them and come to the floor to discuss them."

Reid said Tuesday that "of course" he will allow senators to introduce amendments to the sportsmen bill. But he's reneged on such vows several times this year, usually resulting in the swift defeat of a bill amid Republican complaints that Democrats are blocking up-or-down votes on amendments.

Regardless, Sen. Richard J. Durbin (D-Ill.), said he's eager for another debate about gun control. "I want this debate. I want an opportunity to raise important issues about gun violence and gun safety in America," he said Wednesday morning. Durbin said he would introduce an amendment to stiffen penalties for gun straw purchasers, or people who buy guns for someone else who plans to use the firearm to commit a crime.

Sen. Richard Blumenthal (D-Conn.), whose state is still reeling from the Newtown shooting, said that he and other Democrats were also discussing plans to introduce a proposal to curb gun violence. The hunting bill is "innocuous," he said, and "the failure to address gun violence is a gaping unacceptable omission" from the bill. "We should not be in effect expanding the use of guns without addressing gun violence," he added.

Blumenthal was among 11 Democrats who voted against proceeding with the sportsmen bill Monday night, objecting to its lack of gun-control proposals at the start.

Sen. Tom Coburn (R-Okla.) was the only Republican to vote against proceeding because he had introduced several amendments designed to make changes to how hunters access and pay to use federal lands. He also wanted to amend the bill to limit when military veterans would be restricted from owning firearms because of mental illness.

Other Republicans who are co-sponsoring the bill are poised to introduce amendments to expand gun rights — if Reid ever allows them to be considered.

Aides to Sen. Rand Paul (R-Ky.) said he plans to unveil an amendment that would overturn D.C.'s ban on large-capacity magazines and assault weapons and allow gun owners to carry firearms into post offices and other federal buildings and sites. Aides to Sen. Ted Cruz (R-Tex.) said he has amendments that would allow expanded interstate transport and sale of ammunition and firearms — proposals that are similar to language included in the bipartisan gun-control measure that failed last year.

Gun Owners of America, a leading pro-gun group, said this week that other Republicans, including Sens. John Cornyn (Tex.), Mike Lee (Utah) and Roger Wicker (Miss.) are also prepared to introduce "genuine pro-gun amendments." Spokesmen for some of the senators didn't return requests for comment. The group has described the sportsmen bill as a "nothing-burger" designed to prop up vulnerable Democrats.

Aides to Hagan noted that 40 hunting, fishing or outdoors groups, including the National Wildlife Federation, the Campfire Club of America and the Archery Trade Association, support the hunting bill. But the Humane Society is a vocal opponent of the legislation, in part because it would allow Americans who hunt for polar bear in Canada to import the trophy heads — a long-sought change in federal law. The group, much like Gun Owners of America, described the bill as a political stunt.

"This is Congress as its worst," the group said, faulting Democrats for giving Hagan, Pryor and the other vulnerable Democrats "a political talking point as they campaign in the rural areas of their states."

CORRECTION: An earlier version of this report incorrectly suggested that D.C. has a blanket gun ban. The District bans large-capacity magazines and assault weapons and has strict registration requirements for handguns and long guns.