In a speech to the US Chamber of Commerce, President Lee Myung-bak also said the pact would spur investment and create jobs in both countries, and strengthen the US-South Korean alliance.

Lee is on a state visit to the US. On Thursday he will be received at the White House and become the first South Korean leader in 13 years to address a joint meeting of Congress.

Congress is expected to approve the pact on Wednesday — four years after it was first agreed by the two governments — and also trade agreements with Panama and Colombia.

The Korean free trade agreement is America’s biggest since the 1994 NAFTA pact with Canada and Mexico. The Obama administration says it will increase annual exports of American goods by up to $11 billion and support at least 70,000 American jobs.

“This economic alliance will promote free trade and send a powerful message to the world that the United States and South Korea stand together in rejecting protectionism and that we are open to free and fair trade,” Lee said.

The pact must now be approved by South Korea’s legislature, where Lee’s party has a comfortable majority and passage is expected.

In his speech, Lee said there are those who oppose the pact, believing it would cost jobs, but he predicted they would be proved wrong within a year.

He also said the pact comes at a critical juncture for the global economy with growing uncertainty that problems in the eurozone could precipitate a crisis comparable to the 2008 slowdown.

Lee called on European leaders to come up with a viable solution to prevent the impact spreading to other economies by the time leaders of the G-20 leading advanced and emerging economies meet in Cannes, France, in early November.

South Korea, a founding member of the G-20, is the world’s 12th largest economy. Its trade with the US, the world’s largest economy, amounted to $90.2 billion last year.