UPDATE 1-U.S. launches probe of Boeing dumping, subsidy claims vs Bombardier

(Adds commerce secretary quote, details on case)

SEATTLE, May 18 (Reuters) - The U.S. Commerce Department said on Thursday it was launching an investigation into claims by Boeing Co that Canadian plane maker Bombardier Inc dumped CSeries jetliners in the U.S. market and is being unfairly subsidized by the Canadian government.

The Commerce probe, which was expected, parallels an investigation by the U.S. International Trade Commission into Boeing's allegations that Bombardier sold 75 CSeries planes to Delta Air Lines Inc last year at a price well below cost. Bombardier has refuted the allegations, and the two sides clashed at an ITC hearing on Thursday.

"While assuring the case is decided strictly on a full and fair assessment of the facts, we will do everything in our power to stand up for American companies and their workers," Commerce Secretary Wilbur Ross said in a statement.

The move came as the Commerce Department on Thursday announced its intent to renegotiate the North American Free Trade Agreement between Canada, Mexico and the United States. The move was unrelated to Boeing's petition but reflected President Donald Trump's "America First" policy to make trade agreements more equitable for the United States.

Boeing asked the United States last month to impose duties on the new Bombardier aircraft.

Commerce said that if the investigations determine that CSeries planes were dumped in the U.S. market or unfairly subsidized, it would collect duties equal to the value of the benefits. (Reporting by Alwyn Scott; Editing by Andrew Hay)