FACTBOX: U.S. missile shield in eastern Europe

WARSAW (Reuters) - Poland looks set to agree on Thursday to host 10 ground-based rocket interceptors as part of the U.S. global missile defenses.

The shield project, which also envisions a radar facility in the neighboring Czech Republic, is meant to defend U.S. and European targets against ballistic attack from what Washington calls "rogue states" like Iran.

The Czechs have already signed up to the plan. Parliamentary ratification will be needed in both countries.

Following are some details about the missile shield.

THE PERCEIVED THREAT

* General Henry Obering, head of the Pentagon's Missile Defense Agency (MDA), has said U.S. intelligence suggests that by 2015, Iran could follow North Korea's example and develop a long-range missile capable of striking the United States.

* The United States brought an earlier anti-missile umbrella, based in Alaska and California, on line in 2004 to protect against the perceived North Korean threat. The Czech and Polish sites would augment that system.

* Washington has tried to quell concerns in Moscow that the system would pose a threat to Russia by highlighting that the shield's missiles are defensive only -- carrying no warheads -- and would be no match for Russia's nuclear arsenal.

* The Kremlin still opposes the project.

THE TECHNOLOGY

* The proposed $3.5 billion system would use "hit-to-kill" technology in which an array of sensors and radar would detect an enemy missile in flight and guide a ground-based interceptor to destroy it.

* Without using explosives, the interceptor would ram an incoming warhead at a closing speed of 15,000 miles per hour (24,000 kph) in a process likened to hitting a bullet with another bullet in space.

* The MDA says tests show the technology is sound. But critics, including the Washington-based Centre for Defense Information, say the evidence is misleading, many tests were made in controlled circumstances not resembling real attacks, and more results are needed to prove the system works.

THE PLAN

* The radar installation in the Czech Republic would aim its coverage towards the Middle East to detect a missile in flight and guide interceptor missiles into the trajectory of the approaching warhead.

* Washington has proposed placing as many as 10 interceptor missiles with a range of up to 1,800 miles in Poland.

* The missiles would be housed in underground silos in an area about the size of a football field in northern Poland.

* In return for hosting the shield, Warsaw demanded billions of dollars from the United States to upgrade its air defense systems.

* If approved, construction on both sites could begin in 2009, and could begin functioning in 2011-2013.

(Compiled by Gabriela Baczynska, editing by Tim Pearce)