The two countries are trying to resolve concerns raised by US auto and beef industries that are blocking congressional approval of the pact that some studies said could boost their $78 billion trade by as much as a quarter.

The agreement was signed more than three years ago, and is the largest signed by the United States since the North American Free Trade Agreement (NAFTA) that went into force in 1984.

"The two leaders pledged on a telephone call to work to agree on FTA before the G20 summit as a role model of promoting free trade in the world and upgrading the alliance between the two countries," Lee's office said in a statement.

The White House said on Monday that negotiators would put "maximum effort" to resolve US concerns on autos and beef by the time Obama goes to Seoul. The pair are due to meet on the sidelines of the summit on Nov. 11.

Some US lawmakers have said the deal does not do enough to open South Korea's auto and beef markets. Sales of US autos have lagged behind European and Japanese cars despite imported brands' growing acceptance in the market that is home to the world's number-five carmaker, Hyundai Motor.

South Korean officials have rejected the idea of reworking the deal, saying it already offers a balanced way of expanding bilateral trade that benefits both sides.

Prime Minister Kim Hwang-shik told Parliament on Tuesday that the bottom line for South Korea is there cannot be any revision or renegotiation of the deal that has already been signed.

Meanwhile, British Prime Minister David Cameron will visit China next week with a delegation of ministers before attending the G20 summit, his spokesman said on Tuesday.

It will be the Conservative leader's first visit to China since he took office in May. He visited India earlier this year with a delegation of ministers and businessmen.

Cameron updated his Cabinet of Conservative and Liberal Democrat ministers about the China trip during a routine meeting, the spokesman told reporters.

"There was a discussion about China and the trip next week which is going to be attended by a number of cabinet ministers," the spokesman said.

In a related development, China is ready to work with other countries to achieve balanced economic growth and will seek to perfect its exchange rate system to increase the flexibility of its yuan currency, President Hu Jintao told the French daily Le Figaro in an interview published on Monday.

Hu, who will discuss global economic issues with President Nicolas Sarkozy during a Nov. 4-6 state visit to France, was quoted by Le Figaro as saying it was important to promote fair, balanced trade by fighting protectionism.

"In the future we will continue to perfect, according to the principles of autonomy, controllability and progressiveness, our floating and regulated exchange rate system to make the laws of supply and demand work better and increase the yuan's flexibility, to maintain a relative stability of our currency at a fair and balanced level," Hu was quoted as saying.

He said China's exchange rate policy was "coherent and responsible", adding: "We have always worked to advance the reform of the mechanism of the yuan exchange rate."

Sarkozy is keen to engage China in global talks on economic imbalances and currency fluctuations when France takes over the presidency of the Group of 20 economic powers following a Nov. 10-12 summit of G20 leaders in Seoul.

China holds the world's biggest foreign currency reserves, having accumulated vast amounts of US dollars and euro assets, leading to criticism by US officials that Beijing holds the yuan artificially low against the dollar to support exports.

Asked what China expected to come out of the Seoul summit, Hu said he expected progress in four areas: Reinforcing economic policy coordination; pushing for a reform of the global financial system and reinforcing market regulation; working on global imbalances and fighting protectionism.

"To correct trade imbalances, the parties concerned must transform their mode of development, restructure their economies and promote fair and balanced trade by fighting any form of protectionism," Hu said.

The United States, which runs a huge trade deficit with China, has played down expectations for major progress on resolving imbalances.