Washington  - The Pentagon hopes to carry out a test of its long-range missile-defence system Friday over the Pacific Ocean, the first such test in more than a year of the system planned for deployment to Eastern Europe.

The Pentagon has a launch window of 3pm to 7pm (2000-0100 GMT) but is facing poor weather in Alaska that could force a postponement of the test, said Richard Lehner, a spokesman for the Missile Defence Agency.

If the weather clears up, a target missile will be launched from Kodiak Island, Alaska and radar systems will begin tracking. About 20 minutes later, an interceptor missile from Vandenberg Air Force Base, California will take off on a path to smash into the target missile.

Seven of the 12 tests of the controversial long-range system have been successful, the last one taking place in September 2007. The Bush administration has stepped up the development of long-range missile defence to protect against countries like Iran and North Korea.

But the system still faces technical hurdles, and critics charge the tests do not take place under realistic scenarios.

The Missile Defence Agency rebuffs those allegations. Lehner said the system's crew does not know exactly when the launch will take place. The target missile will also use decoys to try to confuse the interceptor as it nears, Lehner said.

"It's very realistic because the target is carrying the type of countermeasures that we would expect from Iran or North Korea," he said. Countermeasures usually include balloons or chaff. Lehner said the decoys for this test are classified.

The United States has spent more than 100 billion dollars in the last few decades on missile defence. The money has also been used to develop short-and medium-range systems, which have proven more effective in testing than the long-range version.

US plans to deploy the long-range shield to Poland and the Czech Republic have angered Russia, which has threatened to target the sites. The Bush administration planned to install 10 interceptors in Poland and a radar site to the Czech Republic by 2013. But those plans could be scaled back once president-elect Barack Obama takes office in January.

President George W Bush made missile defence a top defence priority. A long-range system has been fielded under his watch in Fort Greely, Alaska and at Vandenberg. (dpa)