CAPE CANAVERAL, Fla. (AP) - NASA will launch an emergency repair mission this fall to the Hubble Space Telescope, which is in danger of shutting down.

NASA decided yesterday to move up the next regularly scheduled Hubble visit to October so astronauts can fix the telescope's deteriorating pointing system. The mission had been set for June 2000.

Two of Hubble's six gyroscopes, needed for pointing and stability, have failed since astronauts' last service call in 1997. And a third gyroscope is partly broken and is considered unreliable.

Astronomers need at least three perfect gyroscopes to conduct observations throughout the universe.

''We are one failure away from losing science,'' said Ed Weiler, head of NASA's space science program.

Although the $2 billion telescope would be safe in orbit without any working gyroscopes, NASA does not want to risk losing any valuable science time.

''This is not a so-called spacecraft emergency where we're in danger of losing the entire mission or the entire spacecraft,'' Weiler said. ''You can think of it more as a science emergency.''

Under the plan, the original 2000 mission will be divided into two parts: the first will be launched around mid-October aboard Discovery and the second in late 2000 or early 2001.

Besides replacing all six gyroscopes in October, astronauts will install a new computer, radio transmitter, guidance sensor and data recorder and fix peeling insulation.

During their second visit, the astronauts will equip Hubble with new solar panels, an advanced camera and a newfangled cooling unit for an infrared camera that has run out of the frozen nitrogen needed for observations.

The four astronauts who will do the repairs have been training since last summer and can easily accommodate the early flight, NASA said.

The extra mission will cost NASA $75 million more than what's been budgeted for Hubble. But Weiler called it ''a rather good insurance policy,'' considering the science that might be lost if NASA were to wait until next summer to make the repairs.Hubble was launched in 1990 with a misshapen mirror. Astronauts corrected the telescope's vision in 1993, restoring Hubble to a capacity to see the fringes of the universe, and returned in 1997 to add or replace 11 major parts.

NASA will have to rearrange the shuttle flight schedule, the details of which have yet to be worked out, to squeeze in the Hubble mission.