By Caren Bohan

ORION TOWNSHIP, Michigan (Reuters) - With support from the South Korean president, President Barack Obama sought on Friday to reassure U.S. auto workers that a new trade pact between the two countries would not cost Americans jobs.

Visiting a General Motors assembly plant in Michigan, Obama said the trade deal signed this week would support at least 70,000 jobs and bolster the U.S. economy.

South Korean President Lee Myung-bak, sporting a Detroit Tigers baseball cap, got a standing ovation from auto workers when he offered a "promise" that the accord that some labor leaders have been wary of would not harm U.S. employment.

"Rather, it will create more jobs for you and your families and it is going to protect your jobs. And this is the pledge that I give you today," he said through a translator.

Before addressing the crowd on the factory floor, Obama and Lee toured the plant, which was at risk of closing before the White House's auto industry bailout.

They sat in the front seats of a new red Chevrolet Sonic, a sub-compact car made with some parts shipped to the United States from South Korea, which Obama said showed the benefits of close ties with the Asian economy as well as the U.S. car sector's comeback from its financial crisis.

In an apparent jab at Mitt Romney, a leading contender for the 2012 Republican presidential nomination, Obama credited the industry's current strength to his own intervention.

"There were a lot of politicians who said it wasn't worth the time and it wasn't worth the money. In fact, there are some politicians who still say that. Well, they should come and tell that to the workers here," the Democratic president said.

U.S. taxpayers extended $50 billion to GM and more than $12 billion to Chrysler in bailout and bankruptcy financing in 2009.

'THE INVESTMENT PAID OFF'

"Today I can stand here and say that the investment paid off. The hundreds of thousands of jobs that have been saved made it worth it. An American auto industry that is more profitable and competitive than it has been in years made it worth it," Obama said. "The taxpayers are being repaid."

The entire bailout included loans and working capital for manufacturers, suppliers and financing businesses that underwrite consumer auto purchases.

The Treasury Department long ago conceded it would likely write off a portion of the bailout. Its latest estimates show the government will recover more than 80 percent of the money.

Romney, a former Massachusetts governor who grew up in Detroit, has said that GM and Chrysler could have been saved without the injection of government funds, drawing criticism from the United Auto Workers union and others.

His 2008 op-ed in the New York Times titled "Let Detroit Go Bankrupt" has haunted him on the campaign trail but reflects a sentiment among many Republicans that Obama spent money too readily when he took office, driving up U.S. deficits and swelling the national debt.

Michigan is likely to be a closely contested state in the November 2012 presidential election.

(Additional reporting by John Crawley and Malathi Nayak; writing by Laura MacInnis; Editing by Deborah Charles and Will Dunham)