Prime Minister Stephen Harper has called a fourth federal byelection for Sept. 22 in the Toronto riding of Don Valley West, setting the stage for a possible general election later this fall.

Voting in three other federal ridings for Sept. 8 was already announced last month by Harper. They include the Ontario riding of Guelph, and Saint-Lambert and Westmount-Ville-Marie in Quebec.

The Don Valley West riding had been held by long-serving Liberal John Godfrey, who signalled his intention to resign the seat some time ago but didn't make it official until Aug. 1.

The Liberals also took Westmount-Ville-Marie and Guelph in 2006 and the Bloc Québécois won the longtime federalist riding of Saint-Lambert in 2004.

There has been speculation that Harper could be gearing up for a general election later in the fall — a possibility that Conservative sources say is still in play.

"This doesn't rule anything out or in," said one senior Tory. "I don't think it changes anything."

He cautioned against reading too much into the move, saying it had been the prime minister's hope to call all four byelections for the same date.

That plan was scuppered when Godfrey delayed his departure, but Harper decided to go ahead once the riding was officially vacant.

"I don't think there's any grand strategy to it," said the Tory insider.

Last week during a Newfoundland and Labrador visit, Harper stoked the campaign fires, complaining that the current House of Commons had become "dysfunctional" and warning that he would "have to make a judgment in the next little while as to whether or not this Parliament can function productively."

The remark was widely interpreted as a hint that Harper, rather than awaiting eventual defeat at the hands of opposition forces, could seize the initiative by going to the Governor General and demanding an election.

Harper also goaded Dion again last week, as he did throughout the spring parliamentary session, suggesting the only reason the Liberals haven't brought down the minority Conservative government is because they're afraid of the electorate.

"Mr. Dion says he doesn't support the government but won't say whether he will defeat us or not," said Harper. "I don't think that's a tenable situation."

Dion has so far refused to take the bait, insisting he will force an election only when he believes the time is ripe.

Current standings in the 308-seat House of Commons are: Conservative 127, Liberal 95, Bloc Québécois 48, NDP 30, Independent 4, vacant 4.

With files from the Canadian Press