The United States is expanding its preliminary missile defense system to address potential threats from the Middle East and China, and from ship-borne missiles off America's coast, the chief of the Pentagon's program said yesterday.

The Pentagon is upgrading radars in Britain and surveying four European countries for a new site for U.S. "interceptor" missiles, to better monitor and defeat incoming strikes from the Middle East, said Air Force Lt. Gen. Henry A. Obering III, director of the Missile Defense Agency.

"We are concerned about the Middle East," he said.

The U.S. military is also cooperating with Japan and other Asian nations to address what the Pentagon considers a growing threat from China's short-range ballistic missiles in the region, while also developing the means to counter an attack by China's long-range missiles.

"What . . . we have to do is, in our development program, be able to address the Chinese capabilities, because that's prudent," Obering told defense reporters at a breakfast meeting.

Closer to home, the Pentagon is studying how to defend against a Scud or other short-range ballistic missiles fired by an enemy from a ship within a few hundred miles of the U.S. coast. The military is focusing on that threat because it experimented with launching a Scud off a ship and found "it was not hard to do," he said.

The ambitious missile defense program -- which has cost $92.5 billion since it began with the "Star Wars" concept of space-based lasers in 1983 -- underwent a major redesign in the early 1990s after the Cold War ended. The system, which is still being tested, is primarily now designed to counter a missile attack from a "rogue state" such as North Korea.

The risk of unforeseen threats from terrorist groups and other enemies is now leading the Pentagon to try to broaden the program's scope, Obering said. "We expect to be surprised," he said, citing the example of North Korea's unexpectedly fast progress in developing long-range missiles.

U.S. commanders have conducted tests on the activation of missile defenses, which have been put on and off alert repeatedly in recent months, Obering said. He estimated that the chain of command would have six to 15 minutes to decide whether to launch intercepts against, for example, a North Korean attack on the United States.

Still, Obering said the costly system suffers from a wide range of technical problems -- from workmanship to software -- and the rush to put it on alert before it is fully tested means the chances are limited that it would succeed in thwarting any missile attack today.

"We have a better than zero chance of successfully intercepting, I believe, an inbound warhead," Obering said. "That confidence will improve over time."

The system is intended to work by shooting into space a ground-based interceptor rocket that releases a "kill vehicle" able to close in on an enemy warhead and destroy it in a high-speed collision. Since 1999, the Pentagon has conducted 10 tests of the system, five of which resulted in hits.

After three failed tests in a row -- including an aborted test in February because of a buildup of salty fog in an interceptor silo -- Obering said he grew "suspicious of some of the workmanship and quality control" in the system. The Pentagon suspended the testing, and teams of scientists uncovered 39 categories of technical problems, Obering said. Boeing Co., a prime contractor on the system, has been penalized "tens of millions of dollars" for test failures that Obering said had been "preventable."

But he said he would rather grapple with the problems of simultaneously testing and fielding the system than face the risk of being unprepared for an attack.

"If we were attacked, the questions would have been: 'Why didn't you get it out there, why didn't you connect the dots?' " he said.

Lt. Gen. Henry A. Obering III heads the Missile Defense Agency.