OTTAWA - The architect of the Conservatives' plan to scrap the long-gun registry says she'll try to build support for her bill right up until Wednesday's crucial vote.

But Manitoba Tory MP Candice Hoeppner conceded Monday that with another New Democrat pledging to vote in favour of keeping the program, her bill is likely dead.

As the House of Commons resumed, New Democrat Peter Stoffer announced he's switching his vote and will now support keeping the long-gun registry in place, despite his long opposition to it.

Hoeppner, who said she'd been trying to reach Stoffer since last week, said she now understood why the Nova Scotia politician hadn't returned her calls.

As she pulled up to Parliament Hill in a white SUV plastered with "scrap the registry" decals, she said she's not hanging up the phone just yet.

"People are very frustrated with members of Parliament who have turned their back on what they campaigned on and what they promised," she said.

"We have a couple of days left, I am hoping some of them — even one of them — will change their mind. That's my job for the next few days."

Hoeppner's bill made it to second reading in the House of Commons thanks to the support of 12 New Democrats and eight Liberals.

But the Commons public safety committee decided it should go no further, after a majority of committee members decided the evidence warranted keeping the program.

MPs will debate the issue Tuesday evening and vote on Wednesday.

The numbers are so close that Prime Minister Stephen Harper and three of his ministers are flying back from United Nations meetings in New York to be present for the vote.

The bill has seen rural and urban Canadians pitted against each other all summer as pro- and anti-registry lobby groups have viciously competed for control of the debate while politicians on the summer barbecue circuit also used it as a rabble-rouser.

The shots kept coming during the inaugural question period of the fall session.

Bloc Quebecois Leader Gilles Duceppe pestered Harper with accusations that he was digging in his heels on the registry to placate his base of western voters, while others accused his government of being on the side of U.S. gun advocates, rather than Canadians.

With the bill likely to fail, the Conservatives have taken to hammering the opposition for turning their back on voters and reneging on campaign promises to scrap the registry.

A Canadian Press-Harris Decima voter-intention survey released Monday suggested the NDP were taking a hit in support because the way their caucus has handled the bill.

The NDP has 14 per cent national support, down six points since April and their lowest level in almost a year. Their biggest losses have occurred among urban and female voters, and among British Columbians.

The telephone poll of 2,023 Canadians was conducted Sept. 9 to 19 and is considered accurate to within plus or minus 2.2 percentage points, 19 times in 20.

Stoffer, who has repeatedly said he was voting in accordance with his constituents' wishes, said changing his mind was one of the most difficult choices he has ever had to make.

But he said his own informal polls of residents in his Nova Scotia riding showed around 60 per cent wanted to keep the program.

"When you have a solemn position for so long and you change it, that never looks good in the public eye," he said.

Liberal Leader Michael Ignatieff has declared that all of his MPs must vote to save the registry on Wednesday.

They will all show up, said Liberal MP Ralph Goodale.

"As far as the Liberal caucus is concerned, we’ll deliver what we’ve undertaken to deliver. It depends although on what all four parties do in the House of Commons," he said.

"We’ll see what the actual count is when the day comes. When that vote is taken, one would hope that the prime minister would take that as a clear indication of the will of the House of Commons and move on."

Of the 12 New Democrats who initially voted in favour of scrapping the registry, Stoffer is the sixth to publicly state he will change his vote.

Five others have been quite public with their desire to end the registry, while one, Manitoba MP Niki Ashton, hasn't said how she'll vote.

Ashton cancelled an announcement about her vote on Friday and none of her offices returned calls on Monday.

But NDP Leader Jack Layton says he has persuaded enough of his MPs to change their vote and thwart the Conservatives.

Stoffer said nobody from his party "cajoled, coerced, twisted my arm" to change his vote.

But he said he was "quite dismayed" that the controversy over whether to keep the registry was framed as a battle between urban and rural Canada.

"There is no question that both sides have played politics on this issue, including myself," he told a news conference.

"I just simply find it unfortunate that it has gotten to this stage."

Stoffer said that if the registry is to stay, improvements need to be made that take into account the best ideas from those who support it and from those who oppose it.

"If we can do that I think we can find a respectful way through this," he said.

Hoeppner didn't rule out having discussions with opposition MPs on amendments to the program, specifically around the issue of licensing.

The NDP has proposed merging the current two types of required licence into one, among other amendments.

But Stoffer said he came to his decision on Saturday after Layton told him Harper had left no room for compromise on the private member's bill.