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By Miyoung Kim and Jack Kim

SEOUL, June 3 (Reuters) - South Korean President Lee Myung-bak said on Tuesday he would not allow imports of U.S. beef from cattle over 30 months without public support, bowing to street protests that have led to a fall in his popularity rating.

Lee is demanding the reworking of a recent deal to allow imports of U.S. beef in South Korea and putting at risk a separate, sweeping trade deal with the United States.

"The President said firmly that as long as the public is worried and the majority does not want it, it is a matter of fact that beef from animals older than 30 months would not be brought in," Lee's spokesman Lee Dong-kwan said on Tuesday.

The demand from South Korea, once the third-largest overseas export market for U.S. beef, could derail the bilateral trade deal as U.S. lawmakers could throw it out unless Seoul fully reopens its market for U.S. beef imports.

Seoul agreed in April to import all cuts of U.S. beef from cattle of any age but on Monday decided to delay resumption of imports due to mounting public food-safety concerns.

"In response to public safety concerns over U.S. beef, the government had asked the United States to stop exports of beef from cattle older than 30 months old," farm minister Chung Woon-chun told reporters.

"Until we receive a U.S. response, beef imports and quarantine inspection will be suspended."

South Korea had planned to publish relaxed rules on U.S. beef imports on Tuesday after delaying the resumption of quarantine inspections from May 15.

Seoul's reluctance until now to acknowledge strong public demand for renegotiation has dealt a big blow to President Lee, who marked his 100th day in office on Tuesday with record low support for a new leader and after days of street protests.

"The ongoing candlelight vigils have been triggered by public concerns over mad cow disease but it has grown to anti-government and anti-U.S. sentiment in the process," Kim Kwang-dong, head of political research body Nara Policy Institute said.

"Beneath this protest there is a strong resistance against the first right-wing government to come to power in 10 years."

SCANT COMMUNICATION

Lee, a former construction business chief executive with a can-do image and the nickname "bulldozer" has been attacked by his critics for pushing ahead with the government plans after scant communication with the public.

A poll by cable news channel YTN showed eight out of 10 Koreans believe Lee was mishandling state affairs and nine people out of 10 think the beef deal should be renegotiated.

Lee, who took office in February with a record victory margin, has been surprised by the nightly protests and his popularity has plummeted over the decision to import U.S. beef.

In agreeing to the imports, he had removed a major obstacle to the U.S. Congress agreeing to the free trade deal that studies say could boost annual $78 billion two-way trade by about $20 billion a year.

But critics said the decision, announced during his visit to the United States in April and just before he met President George W. Bush, was a move to please Washington.

Prior to the agreement, South Korea only allowed in boneless beef from cattle under 30 months of age. South Korea had rejected bone-in beef and certain other materials, such as spinal columns and brains, which it says pose a higher risk of infection.

President Lee apologised last month for ignoring public health concerns and promised to restore the ban if there was a fresh outbreak of bovine spongiform encephalopathy (BSE) or mad cow disease.

BSE is a fatal, brain-wasting disease and is believed to spread through tainted feed. People can catch a human version of the disease by eating contaminated meat.

South Korea imposed a blanket ban on U.S. beef imports for about three years after the mad cow disease outbreak in late 2003. Before then, it imported around 199,000 tonnes worth $850 million of the product a year, the third-largest destination of the U.S. product after Japan and Mexico. (Additional reporting by Park Ju-min; Editing by Keiron Henderson and Valerie Lee) (For related graphic click on: https://customers.reuters.com/d/graphics/KRbeef0608.gif for factbox please see [nSEO222359])

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