By Jon Herskovitz

SEOUL, July 5 (Reuters) - South Korean police said they expect about 35,000 to gather on Saturday for a protest against a U.S. beef import deal and the polices of the new president, whose government has faced a crisis due to the weeks of street rallies.

Polls show that most South Koreans oppose a deal President Lee Myung-bak struck in April to open the market to U.S. beef but about two-thirds of respondents say it is also time to halt the rallies that have grown more violent in recent weeks.

Protest organisers, which include civic groups, religious leaders and a militant labour group that has taken part in some of the most violent street clashes in the country's history, said they expect hundreds of thousands to attend.

The protests began in early May by people worried about possible mad cow disease in U.S. beef but later grew into a forum where a wide variety of people gathered to air their grievances against Lee, who won a December election by a landslide.

Lee has seen his support rate plummet and analysts said he cannot implement reforms such as privatising state-run firms and revamping pension systems unless he can win back the public.

Rallies last weekend left hundreds of protesters and conscripted riot policemen injured, prompting religious leaders to join the rallies in the hopes of calming things down.

South Korean and U.S. trade envoys reworked the beef deal in June with a private-sector agreement that limits trade in beef to cattle under 30 months of age, thought to pose a low risk for mad cow disease, and prohibits shipments of risky parts.

U.S. and South Korean leaders have said there is no scientific evidence that shows the U.S. beef headed to South Korea poses a risk for the brain-wasting disease.

U.S. beef returned this week to store shelves in South Korea, once the third-largest overseas market for the product with sales of about $850 million before Seoul banned sales in 2003 due to an outbreak of mad cow disease in the United States.

Major retailers refused to sell the product out of fear of antagonising angry Koreans, but a few independent butchers who offered U.S. beef quickly sold out of stocks with patrons lining up to buy a product that sells for at least half the price of Korean beef. (Additional reporting by Angela Moon; Editing by Jeremy Laurence)

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