Riyadh ? Over this past year of Arab Spring revolt, Saudi Arabia has increasingly replaced the United States as the key status-quo power in the Middle East — a role that seems likely to expand even more in coming years as the Saudis boost their military and economic spending.

Saudis describe the kingdom’s growing role as a reaction, in part, to the diminished clout of the United States. They still regard the U.S.-Saudi relationship as valuable, but it’s no longer seen as a guarantor of their security. For that, the Saudis have decided they must rely more on themselves — and, down the road, on a wider set of friends that includes their military partner, Pakistan, and their largest oil customer, China.

For Saudi watchers, this change is striking. The kingdom’s old practice was to keep its head down, spread money to radical groups to try to buy peace, and rely on a U.S. military umbrella. Now, Riyadh is more open and vocal in pressing its interests — especially in challenging Iran.

The more-assertive Saudi role has been clear in its open support for the ouster of Syrian President Bashar al-Assad, who is Iran’s crucial Arab ally. The Saudis were decisive backers of last weekend’s Arab League decision to suspend Syria’s membership (though they also supported the organization’s waffling decision on Wednesday to send another mediation team to Damascus).

Money is always the Saudis’ biggest resource, and they are planning  to spend it more aggressively as a regional power broker — roughly double their armed forces over the next 10 years and spend at least $15 billion annually to support countries weakened economically by this year’s turmoil.

The enormous military expansion was signaled last week by Gen. Hussein al-Qubail, the chief of staff. Because of “surrounding circumstances,” he said, the Saudis would spend more to achieve “the highest degree of combat readiness.”

Overseeing the arms buildup will be a new defense minister, Prince Salman bin Abdul-Aziz, described by Saudis as a strong manager during his many years as governor of Riyadh. This contrasts with what foreign analysts say was the loose discipline (and occasional corruption scandals) under his predecessor, Prince Sultan, who died in October after 48 years as defense minister.

Saudi sources provided an unofficial summary of the defense buildup. The army will add 125,000 to its estimated current force of 150,000; the national guard will grow by 125,000 from an estimated 100,000; the navy will spend more than $30 billion buying new ships and sea-skimming missiles; the air force will add 450 to 500 planes; and the Ministry of Interior is boosting its police and special forces by about 60,000. The Saudis are also developing their own version of the U.S. Joint Special Operations Command.

The doubling of ground forces is partly a domestic employment project, but it’s also a signal of Saudi confidence.

The Saudi shopping list is a bonanza for U.S. and European arms merchants. That’s especially true of the air force procurement, with the Saudis planning to buy 72 “Eurofighters” from EADS, and 84 new F-15s from Boeing. The rationale is containing Iran, whose nuclear ambitions the Saudis strongly oppose. But Riyadh has an instant deterrent ready, too, in the form of the Pakistani nuclear arsenal that the Saudis are widely believed to have helped finance.  

Big weapons purchases have been a Saudi penchant for decades. More interesting, in some ways, is their quiet effort to provide support to friendly regimes to keep the region from blowing itself up in this period of instability. The Saudis have budgeted $4 billion this year to help Egypt, $1.4 billion for Jordan, and $500 million annually over the next decade for Bahrain and Oman. They will doubtless pump money, as well, to Syria, Yemen and Lebanon once the smoke clears in those volatile countries.

“In outlays, we’ve budgeted $15 billion a year just to keep the peace,” says one Saudi source, adding up the economic assistance to Arab neighbors. But that’s hardly a stretch for a country that, by year-end, will have about $650 billion in foreign reserves.

The Saudis speak more charitably of the United States than they did a few months ago, after reassuring visits by Vice President Joe Biden and national security adviser Tom Donilon, and close military and intelligence cooperation continues. But President Barack Obama is seen as a relatively weak leader who abandoned his own call for a Palestinian state under Israeli pressure. The U.S. isn’t exactly the god that failed, but its divine powers are certainly suspect in Riyadh.