OTTAWA -- The country's top military commander says he will step down later this year.

Gen. Tom Lawson, who has been chief of defence staff for two-and-a-half years, ended a day of speculation late Tuesday night by confirming he has asked the government not to extend his term in the fall.

"I have informed the government that I would like to retire at the end of my three year tenure as Chief of the Defence Staff," Lawson said in a statement.

"Serving Canada while leading the men and women of the Canadian Armed Forces has been the greatest honour and privilege in my 40-years of service in uniform. There is much work to be done, and I remain focused on my duties as Chief of Defence. I will do so until a replacement is named."

Officials at National Defence spent much of Tuesday avoiding questions about Lawson's future after a published report said he was on the way out.

Defence sources say his departure has been in the works since late last year and the process kicked into a higher gear after the latest list of promotions and retirements was released a few weeks ago.

Interviews have apparently been conducted with four candidates to replace him, the sources say.

It will soon be up to Defence Minister Jason Kenney to send a recommendation to the prime minister.

Two separate sources say it is possible Lawson could be gone by summer. That timetable would make it easier on the government, which is expected to be in full campaign mode in the fall.

There is no set term for chiefs of defence staff, but the average time has been three years.

All of the sources say a replacement short list includes Lt.-Gen. Jon Vance, the country's operations commander; Lt.-Gen. Mike Day, who represents Canada at NATO's southern headquarters; Lt.-Gen. Marquis Hainse, the commander of the army and Vice-Admiral Mark Norman, who commands the navy.

Lawson was appointed in 2012, just as the Harper government was beginning a deep series of budget cuts that eventually carved $2.5 billion from the annual military appropriation.

He inherited a broken procurement system, which was in the process of being taken over by Public Works bureaucrats. The most notable issue was the botched purchase of the F-35 jet fighter. The program that Lawson championed before being appointed to the top job was the subject of scathing criticism by the auditor general.

When he took over, it was also clear that the government's signature defence strategy -- Canada First -- wasn't properly funded.

"It was a bit of a thankless job," said Phillipe Lagasse, a defence expert at the University of Ottawa. "It was a thankless job when he took in 2012 and in the absence of a significant budget increase, his successor will face the same dilemma."

In the fight with Public Works following the F-35 debacle, National Defence could have lost a lot more ground than it did in terms of decision-making authority, he said.

Lagasse said the credit goes to Lawson, who also managed the budget cuts, and oversaw two major foreign deployments, including the current mission to Iraq.

"With what he had to work with, his record is not something to criticize, in my opinion," he said.