The Persian Gulf sultanate of Oman is set to buy a $2.1 billion missile system built by the U.S. Raytheon Co. as part of a U.S. drive to install a coordinated air-defense system linking the region's Arab monarchies to counter Iran.

Details of the contract, including the type of system involved, have not been disclosed, but Oman has been in the market for a medium-range surface-to-air missile system for some time.

Raytheon executives are expected to sign a letter of intent -- the first step in what's invariably a multiyear acquisition process -- for the purchase of the ground-based system during a visit to Oman by U.S. Secretary of State John Kerry, who arrived in Muscat Tuesday on a Middle East swing.

U.S. officials traveling with Kerry say the deal will enhance the air-defense systems the United States has sold to Saudi Arabia, the United Arab Emirates and other allies in the gulf.

These include Raytheon's Patriot Advanced Capability-3 system, a medium-range system, and Lockheed Martin's Terminal High-Altitude Area Defense, or THAAD, system.

Lockheed Martin, the Pentagon's leading supplier by sales, sold two THAAD units to the Emirates in December 2011 for $1.96 billion.

That was the first foreign sale of the system, which can engaged short-, medium and intermediate-range ballistic missiles and can work in tandem with PAC-3 units.

It's also the only functioning system in use that can intercept targets inside and outside Earth's atmosphere although Israel's Arrow-3 system, now under development by Israel Aerospace Industries and the U.S. Boeing Co. will reportedly have that capability too.

Saudi Arabia, whose air-defense net consists of 49 PAC-2 Patriots, MIM-23B Improved Hawk and French AMX-30SA batteries, has expressed some interest in THAAD, and so has tiny gas-rich Qatar.

Dennis Cavin, Lockheed's vice president for army and missile-defense programs, said recently other member states of the Gulf Cooperation Council -- Saudi Arabia, the United Arab Emirates, Kuwait, Qatar, Oman and Bahrain -- are also enthusiastic about THAAD.

In recent months, the U.S. Defense Department has notified Congress of possible contracts totaling more than $11.3 billion with GCC states, including Qatar and Kuwait, to bolster their defense capabilities against Iran.

Among the proposed sales is a $4.2 billion package for Kuwait for 60 Raytheon PAC-3 Patriot missiles and related systems to counter Iran's ballistic missile threat.

There's also a proposed $9.9 billion PAC-3 deal for gas-rich Qatar, which hosts the largest U.S. military installation in the region, the al-Udaid airbase.

The Americans are reportedly planning to install in the emirate a high-powered Raytheon AN/TPY-2 X-Band radar unit that's capable of detecting missile launches at extreme ranges.

This would triangulate with similar units deployed in Israel's Negev Desert and in Turkey that would be able to spot missile launches anywhere in northern, western and southern Iran.

The gulf monarchies' interest in air-defense systems, heartily encouraged by the United States, has created a new multibillion-dollar focus regarding military capabilities in the region.

"The U.S. major defense industries, IT firms, integration systems -- they all have an enormous opportunity," said William Cohen, a former Republican senator who served as secretary of defense during the Clinton administration and now advises U.S. businesses,

"There's a very legitimate concern about Iran being a revolutionary country. Beyond Iran, you have terrorism, cyberattack threats ... you see the implications of the Arab Spring. Every country wants to make sure it's protected against that."

The Americans have long sought an integrated missile defense system within the GCC but the member states continue to be plagued by traditional rivalries and jealousies that negate such a collaborative effort.

However, the awareness of the current Iranian threat, less concerned with a possible nuclear component and more with the ballistic missile dangers, has concentrated the minds of the GCC's strategic planners.

The oil-rich United Arab Emirates, increasingly a military heavyweight in the gulf, has been the leader in this regard.

It's seen by the Americans as the logical command center for this putative antimissile shield.

But these dynastic rivalries have held this project back for years, possibly to a critical degree.

So the Americans will need to focus on eliminating this impediment by persuading the gulf powers to coordinate and share early warning data and interceptor systems to cover the entire region.