(Previously SEOUL, recasts with call taking place)

WASHINGTON, June 7 (Reuters) - U.S. President George W. Bush and South Korean President Lee Myung-bak discussed solving a dispute over importing American beef amid widespread fears there about food safety, the White House said on Saturday.

Lee, bowing to political pressure and mounting street protests against a deal reached in April to fully reopen its market to U.S. beef over safety concerns, has said he would not allow in meat from cattle over 30 months old.

"President Bush assured President Lee that the United States government is cooperating closely with the South Korean government and ready to support American cattle exporters as they reach a mutually acceptable solution with Korean importers on the beef trade," White House spokesman Gordon Johndroe said. He declined to provide further details.

The South Korean government this week postponed resuming imports for the second time since signing the deal and said it would try to find a way to exclude beef from older cattle, which the public sees as more dangerous, from entering the country.

But Lee has refused to give in to demands that his government renegotiate the deal because such a move would backfire and cause "tremendous problems" for South Korea's export-dependent economy.

"President Lee Myung-bak said South Korean consumers are concerned about the safety of U.S. beef," the presidential Blue House said in a statement after the 20-minute phone call.

"He asked for substantive and effective measures that South Koreans can trust that will prevent beef from cattle older than 30 months old from being imported."

SEPARATE FREE TRADE DEAL

Lee has seen his approval rating plummet to 20 percent since winning office in a landslide in December. Thousands have taken to the streets daily to protest the deal and more than 60,000 protested Friday night calling for his ouster.

Lee began a single five-year term in February.

The dispute over U.S. beef imports has wider implications because it could derail a separate free trade deal between the two countries that studies said could boost two-way trade by $20 billion annually.

Lee and Bush also discussed that pact during their call on Saturday and Bush expressed "his strong commitment to secure promptly congressional approval," Johndroe said.

Uncertainties about the future of the Korean beef market, which was the third-largest U.S. export market with an annual turnover of $850 million a year, have fueled opposition among some U.S. lawmakers to the broader trade pact.

South Korean opposition lawmakers have boycotted a new session of parliament, dealing a blow to Lee and his plan to push sweeping economic reforms.

They have also threatened to shelve the U.S. free trade agreement until Lee's government renegotiates the beef deal.

South Korea imposed a blanket ban on U.S. beef imports after an outbreak of mad cow disease in 2003. It briefly allowed in boneless beef from cattle under 30 months of age before suspending that last year after finding bone chips in shipments. (Reporting by Jack Kim in Seoul and Jeremy Pelofsky in Washington)

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