WASHINGTON — A minor software glitch led to a recent test failure of the U.S. missile defense system in Alaska and the Pacific, said Air Force Lt. Gen. Henry “Trey” Obering, director of the Missile Defense Agency.

The software can be fixed by changing “one line of code” in the system, he said Jan. 12 during a telephone news conference.

The Dec. 15 test of the Ground-based Midcourse system failed when the interceptor rocket carrying a nonexploding warhead did not take off as planned. An analysis of computer data from the failed test showed that the acceptable rate of information flow from the flight control computer to the thrust vector controllers on the rocket — mechanisms that control the pitch and yaw — were set too high, Obering said.

“It was too restrictive,” Obering said of the information flow level set by officials. “We did this to ourselves. It turns out we can relax the constraints without any effect on the booster flight.”

The agency will repeat the failed test in February, he said. The software code will be fixed by the rocket’s maker, Orbital Sciences Corp., Dulles, Va. Similar fixes will be carried out to the rockets already in silos through their “umbilical” systems, Obering said.

The December test, called IFT 13C, was the first to use a realistic booster rocket, similar to the ones that have been placed in silos. Earlier tests used Minuteman III rockets, which are considered slower than the rockets that will be used by the missile defense system. The December test was expected to prove that the Exoatmospheric Kill Vehicle — the nonexploding warhead that sits on top of the rocket — can perform as designed with the new rockets.

During 2005, the agency also plans to conduct four more tests:

Two to check radar performance.

One in which a U.S. Navy Aegis destroyer will act as the primary control center.

One test where the target will be launched from Alaska and an interceptor from the Vandenberg Air Force Base, Calif., for the first time.

Only two of these five tests in 2005 will aim to shoot down a target.

Obering said the test failure on Dec. 15 will not affect the eight interceptors that are already in silos — five in Alaska and three in California. But he declined to say when the Pentagon or the White House will declare the system operational.

The Defense Department had hoped to declare the national missile defense interceptors operational by the end of last year, but now does not expect to make an official declaration any time soon, according to Lawrence DiRita, the Pentagon’s top spokesman.

“There has been some expectation that there will be some point at which it is operational and not something else, and I just don’t think people should expect that for the near term,” DiRita said during a Jan. 13 press conference at the Pentagon. “We’re not marching toward a particular date on which we will say the system is now operational.”

Agency officials say the system, which is spread out from Alaska in the north to the Kwajalein Atoll in the South Pacific, represents a test bed that can be pressed into service if a need arises.