On the face of it, Saudi Arabia's reported plan to buy up to 270 Leopard 2E main battle tanks from Spain for $4.17 billion seems odd since Riyadh is expected to get U.S. arms worth $60 billion over the next decade.

Most of those weapons systems are intended to build up the military power of Arab states in the Persian Gulf to counter an expansionist Iran.

But, as Saudi leaders found out when they sent their military to fight rebellious tribes in North Yemen in 2009, they also need weapons to fight insurgencies in rugged terrain.

Saudi Deputy Defense Minister Prince Khaled bin Sultan arrived in Madrid Monday for discussions with Prime Minister Luis Rodriguez Zapatero.

The Spanish daily El Pais reported Sunday that the Leopard sale was on the agenda. If the deal is signed, it will be a record for Spain's defense industry.

Spain signed a military cooperation deal with Saudi Arabia in 2008. This has focused on training pilots of the Saudi air force on the Eurofighter Typhoon at the Moron Air Base in Seville, southern Spain.

A Saudi lieutenant colonel was killed Aug. 24 when his Typhoon crashed shortly after takeoff at Moron. Spain is part of the international consortium that builds the Eurofighter.

The Saudi air force has also set up training programs in Spain for the 72 Boeing F-15S aircraft that Riyadh will acquire under the U.S. arms deal.

According to military analysts, the 69-ton Leopard proved its ability to wage irregular warfare in Afghanistan where U.S. and NATO forces are fighting Taliban guerrillas and al-Qaida jihadists.

Canada bought 100 Leopards, armed with Rheinmetall 120mm L/55 main guns, from the Netherlands to beef up the firepower of its forces in Afghanistan.

Designed by Germany's Krauss-Maffei Wegmann, the Leopard was the main armor component of the German army. The Leopard 2E produced by General Dynamics' Spanish affiliate is a variant of the German Leopard 2 tailored to the requirements of the Spanish army.

It is built by Santa Barbara Sistemas of Spain, which merged with General Dynamics Corp. of the United States in 2003. All told, 219 2Es have been sold to the Spanish military.

The U.S. arms package for Saudi Arabia, which is heavily weighted toward beefing up Saudi capabilities against Iran, includes 72 UH-60 Black Hawk helicopters built by Sikorsky Aircraft and as many as 60 Boeing AH-64D Longbow Apache attack helicopters.

The Longbow is the U.S. Army's principal anti-tank helicopter, capable of firing laser-guided or all-weather air-to-ground missiles. But they are also deadly against insurgent forces.

The U.S. deal also includes 36 Boeing AH-6M Little Bird helicopters that are ideal platforms for counterinsurgency operations. The agile craft is used by U.S. Special Forces for surveillance, as well as inserting or extracting small commando teams swiftly and surreptitiously.

To be sure, Riyadh's overriding concern is Iran's regional ambitions and its alleged quest for nuclear weapons.

But the fighting against Shiite Houthi rebels in Yemen, launched to back up a faltering regime in Sanaa that was unable to crush the insurgency, starkly demonstrated the Saudis' lack of weapons for counterinsurgency warfare.

The Saudis found that the fighting in the mountainous terrain along the border with northern Yemen demonstrated their ground forces were found to be wanting and were forced to rely on artillery and airstrikes to contain the rebellious tribesmen.

"The Saudi government continues to worry that the insurgency and al-Qaida in the Arab Peninsula (in Yemen) will spill across the border in greater numbers," the U.S. global security consultancy Stratfor observed.

"This is not a fight that requires the latest F-15s, but it is one that requires the Saudi military to function professionally.

"After the Saudi military's underwhelming performance against the Houthi rebels, a push for meaningful reform has gained strength."

The Saudis are also concerned that as the American withdrawal from Iraq moves into its final phase they could find themselves locking horns with Iranian-backed irregulars or Iraqi ground forces on their northern border.