A major free trade deal by the United States and South Korea is stuck in a limbo four years after it was signed as both assemblies struggle to reach a political compromise to bring it to a vote.

The pact could boost the partners' two-way trade by as much as a quarter.

Following are some questions about the bill and where it may be headed.

What is Holding up the Vote?
The U.S. Congress and the White House remain stuck in weeks of negotiations to renew a retraining programme for workers displaced by trade as part of a compromise to bring the trade bills with South Korea, and with Colombia and Panama to a vote.

The White House is demanding a deal to renew the Trade Adjustment Assistance at a level comparable to the now-expired 2009 programme, but many Republicans have balked at the idea, questioning its effectiveness.

South Korea President Lee Myung-bak's government has sent the trade bill to parliament but the assembly has yet to set the date to begin reviewing it.

A majority of the ruling Grand National Party (GNP) support the deal. Some opposition Democratic Party members oppose it, saying a revision to the deal reached in December damaged the interest of South Korean automakers.

The ruling GNP has the number to force it through parliament but does not want to repeat the political embarrassment caused by a previous attempt to do so.

Is There Enough Support Once it Comes to a Vote?
The December revision addressed concerns by U.S. car makers and auto unions that the original deal had favoured South Korean automakers too heavily.

U.S. Trade Representative Ron Kirk said those changes meant winning approval in Congress would no longer be "horribly difficult". But it still faces stiff opposition, including from the AFL-CIO, the main U.S. labour group.

In South Korea, the pact has broad support from the public and from businesses which see it as a chance to enter a greater U.S. market and to buy cheaper imports at home.

In addition to backing from the ruling GNP, some opposition Democratic Party members, who had supported the pact when the former liberal president negotiated it in 2007, are for the deal.

What can cause more Trouble Ahead?
South Korea holds a parliamentary election in April next year and a surprise defeat by the ruling GNP at by-elections two months ago caused concern that it could lose its majority.

The party has to win many votes in its traditional rural stronghold in the southeast. A small but powerful farm lobby has a grassroots network in the region and could influence voting on the trade bill by mobilising public opinion against it.

Farmers say Seoul has not done enough to ensure they will be compensated for the damage that their livelihood will suffer when the market opens to U.S. farm goods under the deal.

The U.S. Congress is expected to be able to start work on the trade bills as early as July. That means it will be difficult for the House and Senate to vote on them before they recess in August. (Reuters)