As US Congress prepares to approve America's biggest ever arms deal, state department spokesman Philip J Crowley stresses that Washington's priority is stability in the Middle East Reuters

The US Congress is poised to give its approval to the biggest arms deal in US history when it signs off on weapons sales to Saudi Arabia worth an estimated $60bn (£39bn).

The sale, under negotiation since 2007, is aimed mainly at bolstering Saudi defences against Iran, which the US suspects will achieve a nuclear weapons capability within the next few years. The transfer of advanced technology, mainly planes, is to provide Saudi Arabia with air superiority over Iran.

The Obama administration is due to send the deal to Congress in the next fortnight. The Senate and House then have 30 days to amend, cancel or approve the deal. If approved, the Obama administration can then take the final steps towards completing the deal.

Members of Congress have been notoriously difficult in regard to arms deals with Saudi Arabia over the last three decades, partly because of lobbying by Israel in the 1980s and 90s and partly as a reaction to the 9/11 attacks orchestrated by the Saudi-born al-Qaida leader, Osama bin Laden. They have also raised concerns over the lack of human rights and freedom for women in Saudi Arabia. Congress has amended and even blocked arms deals with the Saudis in the past.

But Washington-based analysts say such concerns will be overridden because of the greater worries about Iran.

A US defence official told Reuters today that the US and Saudi Arabia are discussing a package that includes 84 new F-15 fighter jets, upgrading another 70 of them as well as buying 72 Black Hawk helicopters built by Sikorsky Aircraft, a unit of United Technologies Corporation.

The two sides are also discussing a package for the kingdom's navy.

The Saudis have agreed to an initial $30bn in sales, with another $30bn still under discussion. The initial figure to be sent to Congress for review may be $30bn for approval this year.

The deal rivals the al-Yamamah deal between the UK and Saudi Arabia signed in the mid-1980s, one of the biggest in history, worth $66bn in revenue for BAE.

Michael Knights, the Lafer fellow at the Washington Institute for Near East Policy, who has written in detail about the deal, predicted today a relatively smooth ride from Congress: "The deal has a much better chance of being approved with limited or no modifications.

First, the preparation for the package has been extensive and prolonged, stretching back to 2007. This has ironed out many potential problems, including significant consultations with the Israelis.

"Second, concern about a nuclear Iran is at an all-time high in Washington, Tel Aviv and Riyadh. Third, much has changed in the defence market since the last major Congressional campaign to block or downgrade a major Saudi arms deal, the 1993 Saudi purchase of F-15s aircraft. Since then, US manufacturers have had to up their game to compete with top-tier European technologies that are provided without limitations."

To help ease passage through Congress, Obama is to put the emphasis on jobs, an important consideration at a time of high unemployment in the US. Members of Congress will not want to be seen endangering jobs, especially in the run-up to November's mid-term Congressional elections.

The White House will stress that an estimated 75,000 jobs in companies such as Boeing, Northrop Grumman, Lockheed Martin and General Electric will be protected if the deal goes through.

Some of the weapons systems, in particular upgraded weapons systems, are specifically related to the threat posed by Iran. Details have been leaking out in the US media over the last few months, prompting angry denunciations from Tehran.

Israel, an even closer ally of the US than Saudi Arabia, has also expressed concerned over the transfer of advanced technology to Saudi Arabia.

Addressing Israeli concerns, advanced sensors on the new Saudi F-15s will have technology built in to prevent them being used against their Israeli equivalents.

While Israel sees Saudi Arabia as a useful buttress against Iran, there is a fear in Tel Aviv that a rogue Saudi pilot might opt for a suicide mission against Israel. The Israeli air force want to maintain an advantage.

Knights said: "Iran is certainly the only advanced state that Saudi Arabia needs to fear as a credible armed opponent in the next decade. Certain weapon systems like upgraded missile defences are explicitly concerned with Iran. The advanced sensors in the new Saudi F-15s will have fail-safes to prevent their effective use against US aircraft such as the types used by Israel."

The Pentagon neither confirmed nor denied today that a deal is in the offing. A defence department spokesman restated the formal position: "We have not concluded arms sales agreements with Saudi Arabia, and we have not notified Congress of pending sales. The US does partner with multiple countries in the Middle East in our multifaceted approach to regional security and stability. This involves a wide range of activities from training and exercises to military sales."

Congress has a history of being difficult about Saudi Arabia, passing legislation in 1986 to block sales of missiles and missile launchers approved by President Ronald Reagan. The deal finally went through only after Reagan was forced to withdraw Stinger missiles from the package.

In 1990, the administration of George H Bush planned to send Saudi Arabia $20bn in arms but opposition from Congress saw this cut down to $7bn.