By David Ljunggren

OTTAWA (Reuters) - Canadian Prime Minister Justin Trudeau will visit three major U.S. cities next month to bolster support for NAFTA as negotiators revising the trade pact tackle major differences, officials said on Friday.

The timing of Trudeau's Feb. 7-10 trip is significant, since it comes after a sixth and penultimate round of talks in Montreal from Jan. 23-29 that Canadian insiders are billing as critical.

Canadian sources last week said they were increasingly convinced that President Donald Trump would fulfill a long-standing threat to pull out of NAFTA, which he blames for job losses and a big trade deficit with Mexico.

Trudeau's office said the prime minister would visit Chicago, San Francisco and Los Angeles "to further strengthen the deep bonds" between the two nations.

One Canadian source familiar with the planned trip said it had been in the works for many months and described it as a continuation of Canada's outreach campaign in the United States to sell the merits of free trade.

The source said one goal of the trip was to build up support for NAFTA, saying Ottawa was pleased that more and more Americans were speaking up in favor of free trade.

U.S. industry groups have become increasingly vocal in recent weeks, pressuring the administration to keep NAFTA intact on the grounds that announcing a withdrawal would cause chaos.

Trump told Reuters on Wednesday that terminating the pact would result in the "best deal."

Tellingly, Trudeau will give a speech at the foundation established in honor of former Republican President Ronald Reagan, a proponent of free trade, "to underscore the interconnectedness of the Canada-U.S. economies."

Trump, who also ran as a Republican, has a much more isolationist approach.

Trudeau, who has consistently tried to attract high-tech investment to Canada, will spend time with entrepreneurs in San Francisco. Last year Canada tapped Google parent Alphabet Inc to help plan a mixed-use development in Toronto using advanced digital technologies and urban design.

Trudeau's office did not respond to requests for comment.

(Reporting by David Ljunggren; Editing by Phil Berlowitz)