SEOUL (Reuters) - South Korean police fought with anti-government protesters overnight to break up a rally for former President Roh Moo-hyun, whose suicide a week ago has triggered growing criticism of his successor.

The turnout at the rally late on Saturday, a day after Roh's funeral, was smaller than expected. It had been closely watched in case a massive outpouring of grief for Roh would translate into large street protests against President Lee Myung-bak.

Roh killed himself after becoming embroiled in a corruption scandal. Many South Koreans blame Lee's government for hounding the former leader with the graft probe.

Some students and labor activists fought with police and attacked police buses after they were stopped from entering a city plaza that was blocked with the vehicles.

Close to 20,000 police, many in full riot gear, easily outnumbered the crowd, some of whom stayed on overnight to hold a candle-light vigil. Police rounded up more than 70 protesters.

Roh left office 15 months ago, widely seen as an ineffective leader, with the landslide win of the conservative Lee interpreted as a rejection of a decade of liberal policies.

But Lee has stumbled almost from the start, and he has struggled to push a sweeping economic reform agenda through parliament even though his ruling party has a majority.

Lee's government struggled for several months to contain massive street rallies last year against his decision to open the country to U.S. beef imports which ballooned to a wider protest against his policies.

Analysts said what appears to be growing friction between the liberal and conservative wings of South Korean politics in the wake of Roh's death could act as another break on reform.

Next month parliament is due to vote on a range of key bills including banking reform, more flexible employment laws and easing ownership of media companies, all of which are fiercely criticized by the liberal opposition.