Analysts say Saudi Arabia's biggest concern is that unrest and violence in Iraq will spill over the border, threatening stability in the kingdom.

"The overwhelming desire is for a unified nationalist Iraq and above all for some sort of stability for the Iraqi people," said Anthony Cordesman of the Center for Strategic and International Studies. "The Saudi government has strongly supported the ideas of a national unified Iraq, pushed for reconciliation, avoided taking sides and supported the Iraqi government."

Meanwhile, Saudi authorities worry the influence of Iran -- a predominantly Shiite nation -- on Shiite militias fighting Sunnis in Iraq is threatening the fragile balance of power in the region. Saudi Arabia wants to prevent the repression of Iraqi Sunnis at the hand of the majority Shiite population.

Around 27.5 million Muslims live in Saudi Arabia, which includes the religion's two holiest sites in Mecca and Medina. It holds the world's largest oil reserves and continues to play a dominant role in the region even without directly intervening in Iraq.

In 2003, the Saudi government condemned the United States' intervention in Iraq and refused to contribute troops to the coalition, but since then has allowed U.S. planes to cross its air space to carry out attacks. The government has not directly intervened, despite its interests, in order to maintain a positive relationship with the United States, a major security partner.

"They don't like the increasing Shiite influence in Iraq. They don't like the Iranian influence in Iraq. On the other hand, they're not going to actively support people who are killing Americans," said Gregory Gause III, a Saudi Arabia expert at the University of Vermont in an interview with the Council on Foreign Relations.

Saudi Arabia has become key to Washington's strategy in the Middle East as the United States tries to create an alliance to counter Iranian influence. Saudi King Abdullah has taken the lead in other regional conflicts, notably drafting a plan to resolve the conflict between Israel and the Palestinians.

But the kingdom hasn't given the United States limitless support. In the first sharp rebuke of U.S. policy, Abdullah told regional leaders at the Arab Summit held in March 2007 that "in beloved Iraq, blood flows between brother in the shadow of illegitimate foreign occupation and hateful sectarianism, threatening a civil war."

Joseph McMillan at the National Defense University said that Abdullah's comment put down markers to distance Saudi Arabia from the United States.

"They're trying to be on good terms with the United States, but not so much that they lose their credibility at home or in the Arab world," he said.

The country's longer term interests in Iraq, according to a report prepared for Congress, are to ensure that Iraq's oil industry does not threaten Saudi Arabia's, and to keep Iraq from becoming a military threat to Arab Gulf states.

A stable Iraq also would help prevent the spread of terrorism and create a buffer to Iran, according to Cordesman.

While pledging not to contribute money or military force to the conflict, the Saudi government has acted to ease the humanitarian needs of displaced Iraqis and has hosted regional conferences to deal with the violence.

King Abdullah met with Iranian President Mahmoud Ahmadinejad in early March 2007 to discuss sectarian violence in Iraq, but the meeting did not result in any concrete plans.

While the government sees Iraq as a threat to the regional balance of power, the Saudi public tends to view the conflict in Iraq as a sectarian struggle and the American intervention as the occupation of Arab land, according to Gause.

Individuals are contributing to the conflict by volunteering as insurgents despite the government's attempts to stop influential clergy from encouraging young Saudis to fight.

Still, the number of Saudis joining the insurgency is low when compared to the number of Iraqis fueling the violence. In an April 2006 Center for Strategic and International Studies report, Nawaf Obaid, an adviser to the Saudi government, estimated that 512 Saudis, or 10 percent of foreign fighters, helped the insurgency in Iraq from the beginning of the U.S. invasion, in March 2003, until March 2006, according to Brookings Institution's Iraq Index.

The Saudi government has invested $1.8 billion in closing its northern border with Iraq, the report said. Units patrol around the clock and the government has plans to install a security fence along the border to "keep bad people from going in both directions," said McMillan at the National Defense University.

Saudi individuals also contribute money to the insurgents, though the amount is hard to estimate and transfers are difficult to trace to single countries.

For its part, the Saudi government has pledged $500 million in reconstruction aid to Iraq as of Dec. 31, 2006.

But so far, the Saudi government has not forgiven Iraq's $9 billion debt accumulated during Saddam Hussein's regime, despite calls from the United States to do so, according to the Congressional Research Service.

As the U.S. Congress debates future policy in Iraq, Saudi Arabia has urged the United States not to withdraw troops and has expressed support for President Bush's increase in troop levels.

Saudi Arabia's future role in Iraq could depend on the Bush administration's policy. In December 2006, King Abdullah told Vice President Dick Cheney during a meeting in Riyadh that Saudi Arabia might financially support Iraqi Sunnis if the United States pulls out.

Obaid, at the time an adviser to the Saudi government, wrote in a November 2006 Washington Post op-ed that Saudi Arabia would intervene following a U.S. withdrawal.

The Saudi government disavowed Obaid's column and he was fired from his government position, but his op-ed emphasized the high stakes Saudi Arabia faces in the region.

"To turn a blind eye to the massacre of Iraqi Sunnis would be to abandon the principles upon which the kingdom was founded," Obaid wrote. "It would undermine Saudi Arabia's credibility in the Sunni world and would be a capitulation to Iran's militarist actions in the region."

-- By Anna Shoup, Online NewsHour