By Angus McDowall and William Maclean
RIYADH/DUBAI (Reuters) - Saudi Arabia's warning that it will downgrade its relationship with the United States is based on a fear that President Barack Obama lacks both the mettle and the guile to confront mutual adversaries, and is instead handing them a strategic advantage.
Riyadh is locked in what it sees as a pivotal battle over the fate of the Middle East with its arch-rival Iran, a country it believes is meddling in the affairs of allies and seeking to build a nuclear bomb, charges Tehran denies.
The kingdom's intelligence chief, Prince Bandar bin Sultan, has told European diplomats that Riyadh is contemplating a "major shift" away from the United States over Washington's policies on a host of issues including Syria.
That message reflected the views not just of Prince Bandar, a noted hawk on Middle East issues and outspoken former ambassador to Washington, but of King Abdullah and the rest of the Saudi leadership, diplomatic sources in the Gulf said.
While Saudi Arabia's frustration with the United States was real, and was leading it to explore alternatives to its 70-year dependence on their strategic alliance, nobody seriously thinks Saudi cooperation with Washington will cease, the sources said.
Saudi anger boiled over last week when it renounced a seat on the United Nations Security Council, in protest at what it called international failures to resolve Syria's civil war and grant Palestinians a state.
Behind its concerns was a fear that its closest major ally had failed to respond robustly on Syria and would give away too much in any negotiations it undertakes with Iran, Riyadh's main Middle East foe.
"The Saudis are putting the pressure on so that the Americans stop being so weak," said a Saudi analyst close to official thinking.
"The message is: You need us. And we are not going to play ball with you until you wake up," he added.
Shi'ite Muslim Iran and Sunni Saudi Arabia are at odds on most big struggles in the region, including in Lebanon, Iraq, Bahrain and Yemen. In Syria, Tehran backs President Bashar al-Assad, while Riyadh supports rebels seeking to oust him.
Saudi princes looked on in dismay last month as Obama courted Iran's more moderate new President Hassan Rouhani, reinvigorating negotiations to resolve international suspicions about Tehran's nuclear program.
Despite Rouhani's statements that he wants better relations with the outside world, King Abdullah and other top Saudis remain intensely suspicious about Iran's intentions and whether its new president could even deliver any change.
For Riyadh, the prospect of a U.S. deal with Tehran raises several unappetizing scenarios, including continued Iranian domination over big Arab neighbors such as Syria and Iraq, and an Israel-Iran war with Gulf Arab states caught in the middle.
"It's the Americans' ability to manage the situation that's the problem. It's a bit like back to Jimmy Carter's time. Bill Clinton wasn't like that. He was more able, more active, more of a leader," said the analyst close to official Saudi thinking.
During Carter's presidency, Washington was powerless to stop the collapse of the pro-Western shah in the face of an Islamic revolution that brought to power the Shi'ite clerics Riyadh so distrusts.
The diplomatic source said the Saudis feared the Obama administration was too ready to trust Rouhani on his pledges to improve ties and be more transparent about Iran's nuclear work.
"They fear the Americans will be fooled," he said, and that Washington would allow Iran to become a "threshold nuclear power", allowing it to retain technological capacity that could later be turned to military use.
One particularly worrying possibility for Gulf Arab states is the idea of Israel striking Iranian atomic sites unilaterally if the United States does do a deal with Tehran.
"This puts Saudi Arabia and the Gulf in a very bad position ... they cannot be pro-Israeli politically but they also cannot accept Iran having a nuclear weapon," said the analyst.
Western allies of the kingdom, including Washington, have urged it to reconsider its renunciation of a two-year seat on the Security Council, arguing it will be better able to influence events from inside the body.
"It is difficult to see what they will ultimately get out of it. It's a statement of principle. But it may weaken their ability to gather coalitions and to enlist the help of allies in achieving goals," said Robert Jordan, U.S. ambassador to Riyadh from 2001-03.
One area where Prince Bandar's threat to shift away from the United States could be felt most quickly is in Saudi aid to Syrian rebels.
"What I think puzzles Riyadh is the American position on Syria. The Americans do not see Syria even close to the way the Saudis see it. It's not a priority for them," said Khaled al-Dakhil, a Saudi politics professor and columnist for the al-Hayat pan-Arab daily.
For Riyadh, the outcome of the struggle in Syria will determine whether it, or Iran, ends up with greater influence in the Arab world. The kingdom backs groups it believes are moderate with arms, training, money and logistical support, and has unsuccessfully pressed Washington to join this effort.
Obama is worried that the flow of arms to even moderate groups will end up aiding the militant factions now leading the fight against Assad and has instead urged caution on Riyadh.
Saudi willingness to heed that caution may now change, although it will still avoid backing militant groups.
Saudi Arabia has already fought an insurgency waged by Islamist militants who had returned from jihad in Afghanistan and Iraq and is committed to fighting al Qaeda.
"The opposition has appropriate equipment, but what they are lacking is training. The Saudis have the means of helping with that," alongside allies such as France and the United Arab Emirates, a diplomatic source in the Gulf said.
The analyst said Riyadh was increasingly willing to push its own interests in Syria, much as it did in Egypt this summer, when it backed the army in ousting a moderately Islamist government in defiance of Washington.
"We are going to do our own thing. We are not going to coordinate with the States. We are not going to listen ... when they say 'you can't give weapons to Syria'," he said.
(Editing by Giles Elgood)