WASHINGTON — President Barack Obama signed off today on the first three free trade agreements of his administration, deals with South Korea, Colombia, and Panama that could be worth billions to American exporters and create tens of thousands of jobs.

The three deals were years in the making, and the difficulty of bringing them to fruition make it unlikely there will be another bilateral trade agreement during Obama’s current term.

The accord with South Korea, America’s seventh-largest trading partner, is estimated to support 70,000 jobs.

The agreements will bring to 20 those countries that have free trade relations with the United States.