Despite their deepening political divide, the United States and Saudi Arabia are quietly expanding defense ties on a vast scale, led by a little-known project to develop an elite force to protect the kingdom's oil riches and future nuclear sites.

The U.S. also is in discussions with Saudi Arabia to create an air and missile defense system with far greater capability against the regional rival the Saudis fear most, Iran. And it is with Iran mainly in mind that the Saudis are pressing ahead with a historic $60 billion arms deal that will provide dozens of new U.S.-built F-15 combat aircraft likely to ensure Saudi air superiority over Iran for years.

Together these moves amount to a historic expansion of a 66-year-old relationship that is built on America's oil appetite, sustained by Saudi reliance on U.S. military reach and deepened by a shared worry about the threat of al-Qaida and the ambitions of Iran.

The quiet U.S. moves in Saudi Arabia form part of the backdrop to President Barack Obama's speech Thursday, which is intended to put his imprint on the enormous changes sweeping across the greater Middle East.

All of this is happening despite the Saudi government's anger at Washington's response to uprisings across the Arab world, especially its abandonment of Hosni Mubarak, the deposed Egyptian president who was a longtime Saudi and U.S. ally. The Obama administration is eager to ease this tension as it faces the prospect of an escalating confrontation with Iran over its nuclear program.

Saudi Arabia is central to American policy in the Middle East. It is a key player in the Arab-Israeli peace process that Obama has so far failed to advance, and it is vital to U.S. energy security, with Saudi Arabia ranking as the third-largest source of U.S. oil imports. It also figures prominently in U.S. efforts to undercut Islamic extremism and promote democracy.

The forging of closer U.S.-Saudi military ties is so sensitive, particularly in Saudi Arabia, that the Pentagon and the State Department declined requests for on-the-record comment and U.S. officials rejected a request for an interview with the two-star Army general, Robert G. Catalanotti, who manages the project to build a "facilities security force" to protect the Saudis' network of oil installations and other critical infrastructure.

The Saudi Embassy in Washington did not respond to two written requests for comment.

Details about the elite force were learned from interviews with U.S. officials speaking on condition of anonymity because of the sensitivity of Saudi security concerns, as well as in interviews with private analysts and public statements by former U.S. officials.

The special security force is expected to grow to at least 35,000 members, trained and equipped by U.S. personnel as part of a multiagency effort that includes staff from the Justice Department, Energy Department and Pentagon. It is overseen by the U.S. Central Command.

The force's main mission is to protect vital oil infrastructure, but its scope is wider. A formerly secret State Department cable released by the WikiLeaks website described the mission as protecting "Saudi energy production facilities, desalination plants and future civil nuclear reactors."

The cable dated Oct. 29, 2008, and released by WikiLeaks in December said the Saudis agreed to a U.S. recommendation to create the program after they received an Energy Department briefing on the vulnerability of certain oil facilities.

The program apparently got under way in 2009 or 2010, but it is not clear how much of the new force is operating.

The Saudis' security worries were heightened by a failed al-Qaida car bombing in February 2006 of the Abqaiq oil processing facility, one of the largest in the world. The State Department cable said a subsequent U.S. assessment of Abqaiq security standards determined that it remained "highly vulnerable to other types of sophisticated terrorist attacks." That warning was conveyed to top Saudi officials on Oct. 27, 2008.

"The Saudis remain highly concerned about the vulnerability of their energy production facilities," the cable said. "They recognize many of their energy facilities remain at risk from al-Qaida and other terrorists who seek to disrupt the global economy."

One U.S. official said the Saudi force's mission might be expanded to include protection of embassies and other diplomatic buildings, as well as research and academic installations. The official spoke on condition of anonymity because of the diplomatic sensitivity of the issue.

The newly established specialized force is separate from the regular Saudi military and is also distinct from Saudi Arabian National Guard, an internal security force whose mission is to protect the royal family and the Muslim holy places of Mecca and Medina. The U.S. has had a training and advising role with the regular Saudi military since 1953 and began advising the National Guard in 1973.

The new arrangement is based on a May 2008 deal signed by then-Secretary of State Condoleezza Rice and Saudi Interior Minister Prince Nayef. That same month the U.S. and Saudi Arabia also signed an understanding on civil nuclear energy cooperation in which Washington agreed to help the Saudis develop nuclear energy for use in medicine, industry and power generation.

In October 2008, Ford Fraker, then the U.S. ambassador to Saudi Arabia, called the facilities security force program "probably the single biggest initiative for the U.S.-Saudi relationship" and said the value of contracts associated with the program could reach tens of billions of dollars.

Christopher Blanchard, a Middle East policy analyst at the Congressional Research Service, said the arrangement is important on multiple levels.

"The noteworthy thing is that it's such a sensitive area," he said in an interview. "It's probably the most sensitive area for the Saudis, in the sense that those facilities are the lifeblood of the kingdom."

"It's not only about defending against a single military threat like Iran but also an expression, politically and symbolically, of a U.S. commitment to Saudi Arabia's long-term security," he added. "It's about seeing the U.S.-Saudi relationship into the next generation."

The U.S. had dozens of combat aircraft based in Saudi Arabia from 1991 to 2003. When the planes departed, the U.S. turned over a highly sophisticated air operations center it had built in the desert south of Riyadh.

The U.S.-Saudi relationship has been rocked by a series of setbacks, including the 9/11 attacks in which 15 of the 19 hijackers turned out to be Saudis. Saudi Arabia also is the birthplace of Osama bin Laden, the al-Qaida leader killed by U.S. Navy SEALs on May 2 in Pakistan, and Saudis remain active in al-Qaida in Afghanistan. U.S. officials said this month a Saudi considered the No. 1 terrorist target in eastern Afghanistan, Abu Hafs al-Najdi, was killed in an airstrike. They said he helped organize al-Qaida finances.

Even so, Saudi Arabia has become one of Washington's most valued counterterrorism partners. It also is a top client for U.S. arms. When Defense Secretary Robert Gates visited Riyadh in April, he reaffirmed U.S. intentions to proceed with the deal announced last fall to sell up to $60 billion in weaponry, including 84 F-15s and the upgrading of 70 existing Saudi F-15s.

U.S. officials said the arms deal might be expanded to include naval ships and possibly more advanced air and missile defense systems. The Saudis want to upgrade their Patriot air defenses to the latest U.S. version, which can knock down short-range ballistic missiles in flight. And they have expressed interest in a more capable system designed to defend against higher-flying, medium-range missiles.


Robert Burns can be reached at http://twitter.com/robertburnsAP