(Updates with decision to delay imports)

By Miyoung Kim and Jack Kim

SEOUL, May 14 (Reuters) - South Korea will delay the resumption of U.S. beef imports in the face of mounting public concern over the safety of the product, the farm ministry said on Wednesday.

South Korea, once the third-largest importer of American beef until a U.S. outbreak of mad cow disease in 2003, had been scheduled to start quarantine inspections from Thursday. That would have led to its first full imports of U.S. beef in more than four years.

"I think we need a week to 10 days," Agriculture Minister Chung Woon-chun told parliament.

South Korea reached a deal with the United States last month to open its market wider to American beef. Prior to the agreement, it only allowed in boneless beef from cattle under 30 months of age.

The delay may irritate U.S. lawmakers who have said Congress would not approve a sweeping free trade deal with South Korea unless Seoul fully opened its market to U.S. beef.

The level of public anger over the deal -- which was meant to be a high point of President Lee Myung-bak's visit to the United States last month and his first trip abroad since taking office -- has clearly taken the government by surprise.

Last week, the prime minister and other top officials apologised on national television over the issue and promised to reimpose the ban if there was a fresh outbreak of mad cow disease in the United States.

South Korea imposed a blanket ban on U.S. beef imports for about three years after an outbreak of the disease there in late 2003. Before then, it imported around 199,000 tonnes worth $850 million of the product a year.

Exports from Australia have taken up much of that gap.

Seoul resumed U.S. boneless beef imports from cattle under 30 months last year but even that trade was stopped after quarantine inspectors discovered bone chips and spinal material in several shipments.

South Korea's main opposition party said on Tuesday it would use its last few days in control of parliament to block the free trade deal with the United States unless the new beef agreement is revised.

President Lee's conservative party, which won April's general election, will take control of parliament when its new session starts in early June.

The agreement to reopen South Korea's beef market does not require parliamentary approval, but flare-ups could spill over to the South Korea-U.S. free trade pact, which needs to be ratified by parliament to take effect.

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(Reporting by Jack Kim and Miyoung Kim; editing by Jonathan Thatcher and Sanjeev Miglani)

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