In a shocking move that gave a sudden boost to the minority government while sparking calls of betrayal from the Tories, high-profile Ontario MP Belinda Stronach crossed the floor Tuesday to join the Liberal party.

Stronach, who was considered one of the rising young stars of the Conservative caucus, has joined the Liberal cabinet and was rewarded with the plum portfolio of minister of human resources.

Hours after she first made the announcement, she made it official with a visit to Rideau Hall where she was sworn in.

Her move gives Prime Minister Paul Martin's minority Liberals a better chance of surviving a crucial confidence motion on the federal budget on Thursday, and consequently avoid being forced into a summer election.

"I have been uncomfortable for some time with the direction the leader of the Conservative Party has been taking," said Stronach.

Seated next to Martin at a morning news conference in Ottawa, Stronach said she doesn't see Conservative Party Leader Stephen Harper as being "truly sensitive" to the needs and the complexities of Canada.

"Also, by forcing an election before the Conservative party has grown and established itself in Quebec, the hold over Quebec of the Bloc Quebecois can only grow into the vacuum. The result will be to stack the deck in favour of separatism, and the possibility of a Conservative government beholden to the separatists."

Martin insisted the Liberals didn't woo Stronach with a plum post to win Thursday's budget vote.

"The significance of her decision is not that it necessarily alters the outcome," Martin said, prompting audible snickers at the news conference.

'Betrayed'

"A number of our caucus members are feeling quite devastated, quite betrayed by this," said Harper at his own press conference shortly following the Liberals' announcement.

He said the move obviously makes the defeat of the government on Thursday "much less likely."

But Harper added it "doesn't, in any way, change the principled position that our caucus has taken on this issue that the governing party is corrupt."

Martin said he and the 39-year-old Stronach share common beliefs on questions of policy and politics, including the Gomery commission investigating the sponsorship scandal.

"Based on these shared beliefs, she and I have agreed that she fits more comfortably, can serve more appropriately and can contribute more substantially as a member of the government caucus," he said.

Martin praised Stronach's decision as "courageous," especially in light of the uncertainty surrounding the party as the budget vote looms.

"One vote will not make a difference in Thursday's vote," said Martin. He pointed out that what is so "gutsy" about Stronach's decision is that she made it "knowing that there's the possibility of the fact that we're going into an election campaign."

Stronach admitted the deal was largely brokered by former Ontario premier and Liberal David Peterson after running into him at an event in Toronto Thursday night.

On Friday, they discussed her next move.

Appearing on CTV Newsnet's Countdown, she recounted her conversation with Peterson.

She told him: "I'm thinking about my options within the party, I've been uncomfortable with the direction the leader is taking the party…I just don't feel comfortable lining up with the Bloc to trigger a vote so I'm thinking about my options, thinking about leaving."

Peterson got the ball rolling with the Prime Minister's Office and kept in touch with Stronach over the weekend.

She clinched the deal at 24 Sussex Dr. on Monday night.

Two weeks ago, Stronach warned that teaming up with the Bloc Quebecois to defeat the federal budget in the confidence vote might be a bad move that could backfire on the Conservatives.

She said critical portions of the budget -- particularly the billions promised for municipal infrastructure -- were extremely important to individuals in her riding north of Toronto and other constituencies in the area.

In a question-and-answer session following the announcement, Stronach refused to answer a reporter's questions regarding the future of her relationship with Conservative House Leader Peter MacKay.

Stronach, the former president and CEO of Magna International, made a bold entry into politics by challenging Harper for the leadership of the Conservative Party in 2004.

While she lost that battle, she went on to win the riding of Newmarket-Aurora in Ontario.

The Numbers Game

While Stronach's defection to the Liberals has narrowed the gap, it by no means guarantees the Grits will win Thursday's budget vote.

Before Stronach crossed the floor, the Liberals, with the support of the NDP, had 150 votes. That left them three votes shy of the Conservatives and the Bloc Quebecois, whose combined 153 members planned to vote against the budget.

Now that Stronach has defected, the Liberals and the NDP have 151 votes and the Tories and the Bloc 152.

Carolyn Parrish, a former Liberal MP who now sits as an Independent, has said she will vote with the Liberals, bringing their numbers up to 152.

That leaves the two remaining independents, David Kilgour and Chuck Cadman. If both vote against the budget, the government will fall.

If one votes with the Liberals and the other against, there would still be a tie.

And that would likely be broken in favour of the Liberals by House of Commons Speaker Peter Milliken.

Tory MP Darrel Stinson is expected to be absent because of illness, but the government has said one of its members will sit out the vote if that is the case.