BEIRUT (AFP) - - Lebanese Prime Minister Fuad Siniora heads to Washington for talks with U.S. President George W. Bush, with Beirut caught deep in political crisis and embroiled in a row with former powerbroker Syria.

Siniora's four-day trip comes amid political stalemate over the future of pro-Syrian President Emile Lahoud, the national role of Shiite militia Hezbollah and Damascus's part in last year's killing of former Lebanese premier Rafiq Hariri.

Syrian troops quit Lebanon last year after a near three-decade stay in the wake of billionaire tycoon Hariri's killing. The death sparked massive popular outrage over Damascus's perceived involvement in the plot.

Siniora said he would meet U.S. officials, including President George W. Bush and Secretary of State Condoleezza Rice, and tell them Israel must withdraw from the disputed Shebaa Farms if, as Washington wants, Hezbollah is to be disarmed.

"I will explain to President Bush the necessity of Israel withdrawing from the Shebaa Farms and ending its violations of Lebanese land, sea and air space," he told journalists.

Siniora, who is due to meet Bush and Rice on today, said such a move by the Israelis could lead to Hezbollah's disarmament as the movement says it needs weapons only to defend against Israel.

"The Israeli withdrawal from the Shebaa and the end of Israeli aggression will mean that the state of Lebanon has exclusive use of force on its territory," he said.

UN Security Council Resolution 1559, adopted in 2004, calls for all militias in Lebanon to be disarmed and for Lebanese sovereignty to be respected.

The small mountainous Shebaa Farms territory lies at the convergence of the Lebanese-Syrian-Israeli borders. Israel captured the area from Syria in the 1967 Middle East war, and it is now claimed by Lebanon with Damascus's consent.

Israeli troops have retained control of the area since their withdrawal from south Lebanon in May 2000 after two decades of occupation. The terrain has since become the scene of clashes between Israeli forces and Hezbollah.

Siniora is also to meet FBI chief Robert Mueller to discuss U.S. assistance with investigations into recent politically motivated Beirut bomb attacks. He is also due to tackle U.S. help in bolstering Lebanon's fledgling army with Pentagon officials.

The premier will seek to rally support for an as yet undated international donors conference to aid the stagnant Lebanese economy which currently has a national debt of 38.4 billion dollars, equal to 180 percent of gross domestic product.

A roundtable dialogue of Lebanese leaders being held in Beirut has given Siniora a mandate to normalize fraught relations with Syria, notably by finalizing borders between the two countries, including the Shebaa Farms.

But Damascus insists the current Lebanese parliamentary majority, led by Hariri's son Saad, stop "trying to destabilize Syria by serving the ends of Western plots".

Ahead of Siniora's visit, Hezbollah's chief accused the United States of plotting another civil war in Lebanon.

"America's real plan is to fuel a civil war, while the national plan is for all Lebanese to live in peace with one another," Hassan Nasrallah said.

The United States was at the forefront of UN efforts that forced the withdrawal of Syrian troops in April 2005, and advanced an international probe into the February 2005 murder of Hariri.

Siniora will also head to the United Nations in New York to meet Secretary General Kofi Annan for talks on setting up an international court to judge those behind Hariri's killing.