Prime Minister Stephen Harper has called three byelections for early September, a move that could serve as a possible litmus test for a general election later in the year.

The vacant Quebec ridings of Westmount-Ville Marie in Montreal and nearby Saint Lambert will be up for grabs in the Sept. 8 elections, as will the Guelph riding in Southwestern Ontario.

The Westmount and Guelph ridings were both held by the Liberals, while Saint Lambert went to the Bloc Quebecois in 2004.

Harper had until Saturday to announce the elections, and the earliest possible date they could have been held was Sept. 2.

The elections offer the chance for all parties to generate some political momentum ahead of a possible general election in the fall.

Stephane Dion's Liberals suffered three embarrassing losses in two earlier sets of byelections -- including the former Liberal stronghold of Outremont -- and are desperate to regain some ground. Dion said this week he believes Canadians are now ready for a general election in the fall.

However, Liberal MP Martha Hall Findlay said the party's priority is to focus on the next challenge -- winning seats in the byelections.

"Our plan is to highlight what the Liberal government can offer as an alternative, certainly highlight the strengths of our candidates and highlight the challenges that more Canadians are seeing much more clearly with regard to the Conservative government," she told Â鶹´«Ã½net.

Dion has spent much of the summer trying to sell his Green Shift environmental priorities to Canadians, including his controversial carbon tax plan that would be partially offset by personal and corporate tax cuts.

Hall Findlay played down the notion of the byelections being a referendum on Dion's environmental blueprint -- which includes a controversial carbon tax plan -- saying such contests are often determined by local issues.

She added that the byelections "could also end up being a referendum on the current Conservative government."

"We're pretty confident about the opportunity for Liberal success in all three," Hall Findlay said. 

Dion also suggested the byelections will represent a referendum on Harper's leadership.

A Liberal news release cites Dion as saying the following:

"Canadians will use the three federal byelections called in Quebec and Ontario today to send Prime Minister Stephen Harper a strong message that they don't like the way he is running the country."

The Liberals are running former astronaut Marc Garneau in Westmount, and Frank Valeriote in Guelph -- both Liberal ridings they are desperate to hold onto.

Last year, the NDP's Thomas Mulcair won an upset victory in Outremont -- a loss that set the Liberals buzzing over Dion's leadership capabilities. Mulcair, deputy leader of the party, recently said the party has high hopes to pull off another such win in Westmount.

Dion has so far declined to bring down the minority Conservative government, though multiple confidence votes in Parliament over the past year provided the chance.

However, the party's performance in the byelections could determine whether Dion pushes for a fall vote, or not.

Harper is also likely to gauge support for his party from the results of the fall elections.

Conservative MP Jason Kenney said all three ridings were won by opposition parties in the last election and it will be tough for the Conservatives to gain ground.

But he said he doubts Canadians will endorse Dion's plan and said his performance as Liberal leader will be judged in the byelections.

"It's his record that's on the ballot in these two Liberal-held ridings and we don't think Canadians are accepting Mr. Dion's message that it's time for higher taxes, higher energy prices, higher food prices, higher electricity prices, higher home heating prices," Kenney told Newsnet.

"That's what he wants to do to our economy... he wants to impose a multi-billion dollar tax grab on just about everything."