The source, speaking on condition of anonymity, said continuing discussions among like-minded nations are focused on an air campaign, using mostly Tomahawk missiles, that lasts up to 24 hours.
Foreign Affairs Minister John Baird hinted at such a brief and surgical intervention by the United States during an interview with Quebec's TVA network on Wednesday when discussing the volatile situation in the Middle East.
"That's the reason why if it was a small military intervention, it should be precise — in and out," said Baird, who met in the afternoon with George Sabra, the head of the opposition Syrian National Council.
When host Mario Dumont hypothesized about a strike lasting four days, Baird interjected that it could be as short as two hours.
With Canadian military planes parked at home, and the frigate HMCS Toronto on the other side of the Arabian peninsula lacking long-range missiles, direct involvement by Canada would therefore be improbable, said the NATO source and other military experts.
"Right now in the late, waning days of August, the lead time involved in Canada having any air response is negligible," said Chris Corrigan, a retired colonel and now a defence-security analyst with the Royal Canadian Military Institute.
"A U.S. carrier battle group has as many F-18s on it right now in the Mediterranean ... (as) we have serviceable in the entire Canadian air force."
Baird underscored Canada's limitations when speaking publicly in Montreal, repeating his view that discussing military intervention is premature.
"I think some have speculated in the media and elsewhere that it could involve cruise missiles or armed drones, neither of which Canada has," he said.
"We'll let decisions be made before we know whether we have even the capacity to contribute militarily."
The NATO source said the extent of Canadian military assistance could be dispatching HMCS Toronto closer to the area to help protect American ships, as part of an international naval task force that operates in the Arabian Sea.
Walter Dorn, a professor of defence studies at the Royal Military College, said the frigate could be sent through the Suez Canal to anchor in the vicinity.
"The other possibility is the Americans send their ships off to someplace, and we have to take over some of the original responsibilities of that ship, so we cover for them," said Dorn.
Both Dorn and Corrigan suggested a select number of Canadian Forces personnel could theoretically wind up working inside the American chain of command, as has happened in the past.
"Showing the (Canadian) flag will be very important because the U.S. wants to show this has international legitimacy," said Dorn.
Earlier Wednesday, Justin Trudeau said Parliament should be recalled to discuss what role Canada should play as the international community prepares to respond to atrocities in Syria.
The Liberal leader called the use of chemical weapons "unacceptable" and said it requires a "significant response."
Trudeau, who was briefed Tuesday by Baird on his conversations with allies in the United States, the United Kingdom and elsewhere, said he fully expects Canada will have a role to play in helping civilians.
He said Canadians — and MPs — are united in wanting to provide humanitarian aid and help settle refugees.
But he said anything more than that should be discussed, in a non-partisan fashion, by parliamentarians. Trudeau has previously expressed reservations about military intervention.
United Nations chemical weapons inspectors continued their investigations in a Damascus suburb Wednesday, while Secretary General Ban Ki-moon appealed to the international community to give them more time to complete their work.
But the British government moved ahead with a draft proposal at the UN Security Council authorizing the use of force against Syria, almost certain not to pass because of the opposition of China and Russia.
Russia and Iran have been warning the west that any military intervention could snowball into a greater, regional conflict.
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