10/04/2011 05:03 EDT | Updated 12/04/2011 05:12 EST

Mulcair opts in, Julian opts out of federal NDP leadership contest

OTTAWA - Thomas Mulcair is poised to dive into the federal NDP leadership race.

The Montreal MP had recently hinted he might not take the plunge because party membership numbers in Quebec are stacked against him.

But two Quebec MPs who've already endorsed Mulcair say he's decided to go for it.

Mulcair is expected to officially declare his candidacy in Montreal on Oct. 13.

He's seen as the most serious challenger to former party president Brian Topp, the perceived frontrunner in the contest's early days.

British Columbia MP Peter Julian, meanwhile, has decided not to join the race, despite receiving endorsements from five MPs.

Julian said he concluded he simply couldn't compete with Topp's organizational strength.

"I think it's fair to say that Brian Topp's campaign was out very quickly and has set the bar pretty high in terms of organizational requirements," Julian said in an interview.

"To engage in a race of this magnitude, you need good organizational strength and it just wasn't there (for me)."

Topp was first out of the gate and has racked up an impressive roster of endorsements from party luminaries, including former leader Ed Broadbent, former Saskatchewan premier Roy Romanow, deputy leader Libby Davies and actor Shirley Douglas, daughter of party icon Tommy Douglas.

Mulcair has already gathered endorsements of his own from at least seven fellow MPs from Quebec, despite some doubt about whether he'd actually enter the race. Two of those backers — Jamie Nicholls and Tarik Brahmi — erased any doubt Tuesday.

"I know he's running and I'm happy for that," said Brahmi, confirming that Mulcair has sent out invitations to his formal announcement.

Mulcair is a former provincial Liberal cabinet minister and was the NDP's lone MP in Quebec until last May's election, when the party grabbed 59 of 75 seats in the province. His supporters credit him for the historic breakthrough.

Although Quebec delivered more than half the NDP's record 103 seats, only about two per cent of the party's roughly 87,000 members reside in the province. Mulcair complained that put him at a disadvantage in the one-member-one-vote leadership contest and suggested he might not run as a result.

He seems to have overcome those qualms.

"The membership is low right now in Quebec and we have six months to work on that and that will be our priority," said Brahmi.

Five contenders have so far declared their candidacies: Topp, Quebec MP Romeo Saganash, B.C. MP Nathan Cullen, Ottawa MP Paul Dewar and a little-known Nova Scotia pharmacist, Martin Singh.

At least three others are still weighing their chances, including Toronto MP Peggy Nash, Churchill MP Niki Ashton and Halifax MP Robert Chisholm.

The contest will culminate with a leadership vote on Mar. 24.