Trade policies pursued by President Barack Obama and the Democratic-controlled Congress since the start of the year could lead to the loss of 585,800 U.S. jobs, a study said on Tuesday.

The study done for the U.S. Chamber of Commerce attributed almost two-thirds of the lost jobs, or 383,400, to Congress' failure to approve free trade agreements with Colombia and South Korea.

Obama opposed those agreements during last year's campaign, but has promised to push for their approval once a number of concerns raised by his fellow Democrats are addressed.

The U.S.-Colombia free trade agreement was signed nearly three years ago in November 2006. The pact with South Korea was signed in July 2007, as was a third deal with Panama that Obama also has not yet sent to Congress for a vote.

The study prepared by Trade Partnership Worldwide, an economic consulting firm that specializes in estimating the impact of trade policies, said Buy American provisions of the economic stimulus bill passed by Congress earlier this year were another big source of potential job losses.

If other countries retaliate by shutting American companies out of just 1 percent of their domestic stimulus programs, the net employment loss to the United States from the Recovery Act's Buy American provisions could total 176,800. In the event retaliation escalates, U.S. job losses will mount dramatically, the study said.

Lastly, the Obama administration's failure to resolve a cross-border trucking dispute with Mexico threatens another 25,600 U.S. jobs, the study said.

It based that on the impact of retaliatory duties imposed by Mexico in March and higher shipping costs associating with transferring cargo from Mexican to U.S. trucks.

(Reporting by Doug Palmer; editing by Eric Beech)