Clinton said she's aware of the debate in Parliament about Canada's future contribution to the mission against ISIL, saying Canada has been an "indispensable" ally in the past.
Clinton indicated no preference in her speech at a Canada2020 think tank event, even as the debate on a combat mission to Iraq continued in the Commons.
"The United States, I'm sure, will welcome and respect whatever level of support Canada decides is appropriate to help meet this shared challenge."
Clinton said it will be a long-term struggle that will take a military contribution — she called that "essential" — as well as a propaganda war because ISIL is so savvy on social media.
"We need to fight an information war, as well as an air war," Clinton said afterwards, in question-and-answer session.
In steering clear of Canada's ongoing debate, Clinton was making a break with past. On earlier visits, she expressed outspoken opinions on Canadian policy in the Arctic and the need to stay the course militarily in Afghanistan, which rankled the Harper Conservatives.
As the Obama administration continues to build its anti-ISIL coalition, the Harper government plans to commit fighter planes, surveillance aircraft and support personnel for up to six months.
The mission faces opposition from the NDP and Liberals.
The NDP proposes a different mission. It would give the air force a three-month mandate to fly in weapons to local fighters who are facing ISIL. It would also stress humanitarian aid and investigation and prosecution of war crimes cases.
The Liberals supported Canada's initial military contribution of up to 69 special forces advisers for 30 days.
In the U.S., Clinton said, there is bipartisan agreement on how to deal with ISIL, which is to degrade their capabilities and defeat them.
"The goal itself, that this is a threat, is agreed to in our political system," said Clinton.
"It is a long game. We turn away from it at our peril."
Clinton made waves this past summer when she told a U.S. magazine that the Obama administration should have acted sooner to stop ISIL's advance.
Clinton is widely seen as the potential Democratic front-runner for the 2016 U.S. presidential campaign.
Asked about that, Clinton smiled and said: "I've been dodging this question for a year and half and I'm going to keep dodging it."
She said she is "thinking hard" about a presidential run but won't make her decision until after the upcoming midterm Congressional elections.
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