SEOUL, South Korea — South Korean President Lee Myung-bak pledged to keep U.S. beef out of South Korea unless Washington agrees to ban meat from older cattle, seeking Thursday to defuse a political crisis sparked by health concerns that has derailed his plan to boost U.S. ties and reinvigorate the economy.

In a nationally televised address, Lee said he will "ensure that the U.S. beef older than 30 months will not be put on our dinner tables as long as the people do not want it." Cattle younger than 30 months is considered less at risk for mad cow disease.

The South Korean leader said he had told Bush during a phone call earlier this month that South Korea "would not be able to import U.S. beef" if its demands were not accepted.

Protests prompted by fears of mad cow disease in American beef grew into broader opposition to Lee's policy agenda, and paralyzed his government, as critics blasted him for failing to heed public opinion and accusing him of pandering to U.S. interests. The protests came to a climax with a candlelight rally last week that drew some 80,000 people.

His comments Thursday came as the top trade officials of the two countries held their latest talks Wednesday in Washington where Seoul was seeking to restrict beef shipments to cattle younger than 30 months, which are believed to be less at risk of mad cow disease. The meeting ended inconclusively and the sides agreed to meet again Thursday, Seoul's Foreign Ministry said.

South Korea was the third-largest overseas market for U.S. beef until it suspended imports after the first American case of mad cow disease appeared in December 2003. Restricted imports of U.S. beef reached South Korean supermarkets last year, but shipments were put on hold after banned parts, such as bones, were found in a shipment.

Lee also apologized Thursday over his April decision to allow resumed imports of American beef — made just hours before he met President Bush in Washington — saying he thought it would help passage of a broader free-trade deal with the United States.

"I and the government are deeply sorry" for not caring about what the people wanted, he said.

It was Lee's second apology in less than a month over the beef debacle, which has forced all of his top aides and the entire Cabinet to offer to resign and led to weeks of protests. Lee, a former Hyundai CEO and Seoul mayor, took office in February after a landslide election win last year but has seen his popularity plummet over the beef issue.

With the global economy slowing, Lee said he had viewed the U.S.-South Korea free-trade agreement as a "shortcut" to fulfill his campaign promise to boost the South's economy. "I did not want to miss this golden opportunity," he said.

But "there was no possibility of ratification" this year of the free-trade deal if South Korea continued to reject American beef, he said. The free-trade agreement has been approved by both governments but awaits legislative approval in Seoul and Washington.

Lee, a conservative from the Grand National Party, also said he wanted to improve relations with the U.S. to help the country's security, citing the nuclear threat from North Korea. Ties between the longtime allies had become strained during a decade of liberal governments in Seoul.

The scale of the protest rallies against the deal has markedly dropped since last week as the government began seeking to limit the import deal. Only 800 people turned out for the daily candlelight vigil Wednesday, police said.

Protest organizers said they would keep rallying against the beef deal until Lee announces a complete renegotiation of the accord.

"The president virtually rejected calls for a renegotiating so we can't help but continue candlelight resistance," said Jang Dae-hyun, a spokesman for a coalition of civic groups that have spearheaded the demonstration.

Scientists believe mad cow disease, or bovine spongiform encephalopathy, spreads when farmers feed cattle recycled meat and bones from infected animals. In humans, eating meat products contaminated with the illness is linked to variant Creutzfeldt-Jakob disease, a rare and fatal malady.