WASHINGTON - As the Senate prepares to begin debating new gun control measures, some of President Barack Obama's fellow Democrats are poised to frustrate his efforts to enact the most sweeping limits on weapons in decades.

These Democrats from largely rural states with strong gun cultures view Obama's proposals warily and have not committed to supporting them. The lawmakers' concerns could stand in the way of strong legislation before a single Republican gets a chance to vote "no."

"There's a core group of Democratic senators, most but not all from the West, who represent states with a higher-than-average rate of gun ownership but an equally strong desire to feel their kids are safe," said Mark Glaze, director of Mayors Against Illegal Guns. "They're having hard but good conversations with people back home to identify the middle-ground solutions that respect the Second Amendment but make it harder for dangerous people to get their hands on guns."

All eyes are on these dozen or so Democrats, some of whom face re-election in 2014. That includes Sens. Max Baucus of Montana, Mark Begich of Alaska and Mark Pryor of Arkansas.

The Senate Judiciary Committee begins hearings Wednesday.

Interest groups, lobbyists, lawmakers, crime victims and others with a stake in the outcome will be watching these senators closely for signals about what measures they might support. The answers will say a lot about what, if anything, Congress can pass in the wake of the shootings of 20 school and six adults at an elementary school in Newtown, Conn., last month.

At issue are Obama's proposals to ban assault weapons, limit ammunition magazines, crack down on trafficking and require universal background checks. Leading the charge against those ideas is the National Rifle Association. The group wields enormous power to rally public sentiment and is a particular threat to Democrats in pro-gun states who face re-election.

The political concerns of Democrats create problems for Senate Majority Leader Harry Reid, D-Nev., who has his own history with the NRA.

The powerful gun lobby endorsed him in previous elections, but stayed neutral in his most recent race, in 2010. Even before Obama announced the gun proposals this month, Reid told a Nevada PBS station that an assault weapons ban would have a hard time getting through Congress. That comment irked Sen. Dianne Feinstein, D-Calif., author of such legislation.

"Clearly it wasn't helpful," she said this past week in reintroducing her measure. But Feinstein's original assault weapons ban was a stern political lesson for Reid and other Democrats. Its passage as part of President Bill Clinton's crime bill in 1994 was blamed for Democratic election losses that year after the NRA campaigned against lawmakers who supported the legislation. When the assault weapons ban came up for renewal in 2004, Congress, under pressure from the NRA, refused to extend it.

Reid has pledged action on gun measures. "This is an issue we're not going to run from," he said. But he's under pressure from all sides.

Some major pieces of legislation are shepherded by the Senate leadership to the Senate floor. But Reid is promising that the gun bills will go through the Senate Judiciary Committee, whose chairman is Sen. Patrick Leahy, D-Vt., a gun owner and Second Amendment supporter.

Reid also is promising an open amendment process, potentially a lengthy endeavor. Those signals have some gun control activists concerned that the process will go so slowly that it will grind to a halt without action. Some question whether that's just the outcome desired by some moderate Democrats.

"I'm concerned just because Harry Reid has a mixed record on these things and we want him to be a champion," said Josh Horwitz, executive director of the Coalition to Stop Gun Violence.

On the other side, the NRA, known for rewarding friends and punishing enemies, promises it will be closely watching Reid, too.

"He's going to be torn and a lot of people are going to be torn, particularly Democrats, but I think as the debate goes on he'll do more good than bad from our perspective," said David Keene, NRA president. "All this stuff has been debated before and once you get into a debate and a discussion and say will this do anything to protect children, to prevent another Newtown, I think the answer is going to come out 'no.'"

Baucus, Begich, Pryor and others have been cautious in their comments on Obama's gun proposals.

Baucus called for "a thoughtful debate." Begich told his home state Fairbanks Daily News-Miner that passage of any element of the package was "a long haul. ... There are some of us who just fundamentally believe in a Second Amendment right." Pryor has told Arkansas media that efforts on gun safety should start with enforcing existing laws.

Another Democrat closely watching the issue is Sen. Joe Manchin of West Virginia, known for a 2010 campaign ad where he fired a rifle shot though a copy of Democratic-written climate change legislation. Manchin recently told a West Virginia radio station that he's working on legislation to require background checks on most gun purchases. Details weren't clear but that's the area where advocates are most hopeful of finding a solution that could get through the Senate and possibly even the Republican-controlled House.

The NRA generally opposes legislation mandating universal background checks and disputes gun control groups' claims that 40 percent of purchases happen without such checks. NRA officials question whether background checks could be done effectively in a way that makes a difference and doesn't disrupt legitimate sales.

The NRA's executive vice president, Wayne LaPierre, is to testify Wednesday before Leahy's committee.

Democrats, especially those from gun-rights states, will be weighing whether to side with the NRA or follow the president, or how best to split the difference.

"We're a Second-Amendment state. I support the rights of sportsmen and target shooters and collectors to own firearms. It's an important part of our culture and tradition," Sen. Mark Udall, D-Colo., said in an interview. "But I just hear there's such grave concern given the experiences we've had with Aurora, Columbine ... people all over Colorado want to prevent these massacres."