UPDATE 2-South Koreans protest against beef and Lee

(Adds new figure for number of protesters)

By Jon Herskovitz

SEOUL, July 5 (Reuters) - South Korean police said about 50,000 people protested in Seoul on Saturday against a U.S. beef import deal and the policies of the new president, whose government has faced 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, said they expected hundreds of thousands to attend. There were no major incidents of violence in the first few hours of the rally.

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

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

Rallies last weekend left hundreds of protesters and conscripted riot policemen wounded, prompting religious leaders to join the rallies in the hope 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 body parts.