ALEXANDRIA, Va. (AP) _ A man who shot and killed a Navy officer at a bus stop outside the Pentagon 3 1/2 years ago was found innocent by reason of insanity Wednesday by a federal judge.

The ruling by U.S. District Judge Albert V. Bryan Jr., means that Carl E. Campbell, 30, of Manchester, Ga., could be freed from a federal psychiatric facility if he recovers from his mental illness. But a psychologist determined recently that Campbell remains seriously ill. He has been held at a federal hospital in Springfield, Mo.

Cmdr. Edward J. Higgins, 42, a Navy arms control specialist, was killed on May 30, 1991, as he and several other people waited for a shuttle bus in a Pentagon parking lot.

In court papers, prosecutors said that Campbell, who had been treated earlier for paranoid schizophrenia, believed the U.S. government had implanted a mind-controlling computer chip in his brain. The court papers said Campbell also had sought a meeting with Gen. Colin Powell, then chairman of the military Joint Chiefs of Staff.

After being turned away, Campbell stormed to the parking lot and shot Higgins to ''show his displeasure with the United States government,'' prosecutors said.