A computer false alarm, the second in seven months, prompted U.S. strategic force to start moving into action Tuesday, the Pentagon disclosed yesterday.

The false alarm from the North American Air Defense Command headquarters in Colorado Springs indicated the Soviets had fired missiles at the United States, officials said.

While bombers were started and communications with U.S. missile crews were intensified, commanders checked other sensors and concluded the warnings were bogus.

The error was detected within three minutes, officials said. By that time the White House situation room "was aware of the possible threat," the Pentagon said, but neither President Carter nor Defense Secretary Harold Brown was notified.

No bombers or missiles were launched.

An earlier false alarm was transmitted by North American Air Defense Command warning systems Nov. 9.

Pentagon officials said yesterday that the November warning was caused when a test computer tape simulating a missile attack fed the warnings beyond NORAD to military commands and federal agencies. The mistake was blamed on a mechanical glitch.

The cause of Tuesday's false alarm is under investigation, the Pentagon said.

Tuesday's alarm indicated that the Soviets had launched both land and submarine missiles at the United States, the Pentagon said.

Senior officers at the Pentagon's Military Command Center, at the Strategic Air Command headquarters in Omaha and at the North American Air Control conferred and decided to gear up for a possible response.

"As a precaution and in accordance with standard procedures," the Pentagon said in a prepared statement yesterday, "certain Strategic Air Command and command control aircraft were brought to a higher state of readiness."

Officials said the only plane to take off was an unarmed command and control aircraft from Hawaii.

"The computer technical problems are now being assessed to determine corrective action," the Pentagon said.

Because the Pentagon said after its probe of last November's false alarm that it thought the warning system had been fixed to avoid a recurrence, Tuesday's alarm may prompt a wider probe by the administration and Congress of the reliability of today's strategic warning systems.