OTTAWA, Dec 7 (Reuters) - Canada moved to formalize Statistics Canada's independence as an arms-length agency on Wednesday in an attempt to boost the agency's credibility after its head quit last year in protest over concerns about the agency's autonomy.

The legislation to amend the Statistics Act, introduced to parliament by Innovation Minister Navdeep Bains, would also give the chief statistician a renewable five-year term and create an advisory council to ensure the agency is transparent.

"Our government believes that for a national statistical agency to be credible, there must be a high degree of professional independence," Bains told reporters.

StatCan releases the country's official economic data on everything from jobs to trade in reports that are closely watched by markets and investors.

The agency has been dogged by controversy over its independence from the government, in part because of technological problems the Liberal government inherited from the previous Conservative government.

The agency was criticized earlier this year for technological issues that delayed the release of some economic reports on its website.

StatCan was also forced to withdraw a jobs report in 2014, citing a flaw in the way the figures had been processed. The monthly report can be volatile, often prompting economists to question its validity.

The proposed changes to the law, certain to be passed by the Liberal majority government, were part of the Liberals' 2015 campaign promise to reinforce the agency's independence, which previous had been independent by convention only.

The agency's top statistician, Wayne Smith, resigned in September after complaining for months that the centralization of data services under Shared Services Canada gave the technical branch an effective veto over many decision of StatCan.

The proposed changes would also remove from the Statistics Act the threat of imprisonment for those who refuse to respond to mandatory surveys, replacing the penalty with a fine.

(Reporting by Andrea Hopkins; Editing by Jonathan Oatis)