Bob Rae says he isn't looking for a summer job when he runs for interim leader of the Liberal Party of Canada.

Rae announced his intention to run for interim leader on Thursday, but said in a letter to Liberal MPs, senators and staff that he'll only do it if the job is for 18 to 24 months.

In an interview on CBC's Power & Politics, Rae said he hopes the national board, the party's executive, understands there needs to be a clear period set out for the job.

"If there isn't, if it's just a kind of a summer job, then obviously somebody else can do that," Rae told host Evan Solomon.

"But if the party is serious about wanting to rebuild, if the party is serious about wanting to deal with some of its underlying problems and challenges financially and otherwise, then I'm prepared to undertake that task."

Rae wouldn't say whether he'd try to stay on if things are running smoothly, despite the party's decision not to allow the interim leader to run for the permanent leadership.

"I don't think there's any point in speculating about this," he said. "I'm not running for the long-term leadership. Frankly, I don't think the party wants anybody to be running for the long-term leadership right now. I think the party has made it pretty clear that they want a period of rebuild and they want a timeout."

The only other declared candidate for the interim leadership is Montreal MP Marc Garneau.

But Garneau now says he may step aside in favour of Rae.

Garneau said Rae's candidacy gives him "pause for thought" and that he wants to talk to people who have offered their support before he decides whether to continue.

"They may have supported me because they thought I might be the only person. We'll find out in the next few days," he said.

"Clearly we'll find out next Wednesday. If the great majority of people want Bob Rae to be the interim leader, I'm going to be a good team player and be behind him too."

Liberals to choose leader next week

The reduced caucus of 34 MPs and 45 senators is scheduled to meet next on May 25, which gives interested candidates more time to make a final decision and garner support from their colleagues.

The outcome of that vote will be the caucus's recommendation and that will go to the party executive, which will appoint the interim leader.

Michael Ignatieff triggered the race when he resigned as leader on May 3 after the party lost 43 seats from their total in the last House of Commons.

The party lost Official Opposition status to the NDP and Ignatieff also lost his own seat in Ontario's Etobicoke-Lakeshore to a Conservative.

The party's executive effectively eliminated some candidates from the interim leadership race by setting the rules so the person must be bilingual and must sign a pledge that they will not pursue the permanent leadership.

A source close to Rae said the former Ontario premier says he thinks it's in the best interests of the party that he not run for the permanent leadership.

The source said Rae believes the next leader has to come from outside the current caucus.

But Rae is only interested if the interim leadership is longer than the six months set out in the party's constitution. The Liberal Party announced over the weekend that the party will hold a convention via teleconference next month to change its constitution so that a leadership vote can be put off until at least 2012.

In a letter sent Thursday to Liberal MPs, senators and staff, Rae says he'll abide by any rules about the interim leadership that are agreed to by the caucus and the party's executive, known as the national board.

"I have made it a watchword of my time in public life to practise the politics of unity and principled compromise. I shall continue to do so," Rae wrote.

Rae said the party has to choose between having a leadership contest soon, or rebuilding and then having a leadership contest in 18 to 24 months.

"I favour the second option, and that is the context within which I would accept the appointment as interim leader. If this longer period is agreed to, it is my understanding that the exact timing of the leadership election will be recommended by the caucus to the national board."

Wise to put off race: Graham

Former interim leader Bill Graham, who led the party after Paul Martin stepped aside in 2006, says the party is wise to put off the leadership race for a year or two.

Graham told Power & Politics host Evan Solomon on the War Room podcast that it will be a long process of rebuilding and the party needs an experienced person at the beginning to help this through. 

Graham said the interim leader needs to establish personal credibility because the person will have no real authority and no real power, only the power of persuasion.