By Jon Herskovitz

SEOUL, Jan 14 (Reuters) South Korean and US negotiators will try to overcome massive street protests, acrimony in prior discussions and a ticking clock this week in talks to strike a free trade deal between the two economic powerhouses.

The two sides begin what could be make or break discussions in Seoul tomorrow. With annual two-way trade running at about 73 billion dollars, the chief US negotiator emerged from the last round in Montana last month calling the stuation ''troubling''.

Washington and Seoul have clashed on issues including South Korean barriers to US auto imports and pharmaceuticals and US anti-dumping duties that South Korea believes are often unfairly applied to its products.

Even before the week-long discussions opened in Seoul, there were signs of acrimony.

''As Washington refused to remove or ease its anti-dumping rules, there will be no discussion on autos, medicine and other issues of US concern in the upcoming talks,'' said Han Dongman, a trade ministry spokesman.

The two sides would focus instead on ''less sensitive'' issues such as a tariff phase-out in industrial goods and intellectual property rights, Han said in an e-mail. The top negotiators would hold informal talks on the most contentious issues.

The two sides want to strike a deal early this year before legislation expires on June 30 that allows the White House to negotiate agreements lawmakers can reject but not amend.

The same law requires the White House to notify Congress 90 days before signing any agreement, meaning it needs to have a final deal with Seoul by the end of March.

If South Korea strikes a deal, the increased trade could amount to a net gain of about 11 billion dollars for its economy, according to some studies, and give it a leg up on Asian rivals Japan and China in trading with the world's biggest economy.

The United States stands to see a bigger market for its financial services, information technology and automobiles in South Korea, the world's 11th largest economy in 2005, according to the World Bank.

South Korean farmers, angered at possibly losing government protection under a free trade agreement, are planning to stage rallies protesting against the deal and a separate agreement allowing US beef imports to return to South Korea.

During a round in July 2006, South Koreans armed with metal rods and bamboo poles fought bloody clashes with police in riot gear in protests aimed at upsetting the trade talks.

Another major street protest was planned for Tuesday, said Lee Young-soo, an official with the Korean Peasants League.

''Farmers are worried about a 'big deal' being reached. We know both sides are pressed for time but we want our government to go slow and be careful,'' Lee said.

REUTERS SP HT0927