The Hubble Space Telescope, which revolutionized the study of the cosmos and is considered one of the finest scientific instruments ever constructed, will be forced into early retirement, NASA officials said yesterday.

NASA Administrator Sean O'Keefe told telescope managers and engineers that he was scrubbing the final space shuttle flight that would have installed new scientific instruments and replaced critical targeting and power components.

His announcement, during a meeting at the Goddard Space Flight Center in Greenbelt, came two days after President Bush ordered the space agency to reallocate $11 billion from its five-year budget to focus on sending humans to the moon and beyond.

The National Aeronautics and Space Administration already had plans to retire the Hubble in 2010. But without its scheduled 2006 tune-up, which included the replacement of aging gyroscopes and batteries, officials said the telescope might not last beyond 2007.

That would leave astronomers without a comparable instrument until the more powerful James Webb Space Telescope is launched in 2011.

"People are devastated," said Steven V.W. Beckwith, director of the Space Telescope Science Institute in Baltimore, where 450 scientists, engineers and other personnel coordinate Hubble research for NASA. "This is the most prominent science facility in the world."

NASA officials said they didn't expect any immediate job losses at the institute or at Goddard, which manages the spacecraft itself.

The space agency signed a $162.2 million contract last summer putting the institute in charge of Webb Space Telescope research.

The institute's employees learned of the Hubble decision yesterday afternoon in a hastily called meeting that left many shocked and worried.

"Why would we mothball it?" said astronomer Adam Riess, whose work on exploding stars has relied heavily on the Hubble. Scientifically, he said, the telescope "is still in its prime."

Riess said that in the past year he has discovered seven of the most distant exploding stars, or supernovae, ever recorded.

NASA officials said yesterday that the decision to cancel the final service mission was influenced by Bush's new space initiative, which calls for NASA to complete the International Space Station by 2010.

To meet that deadline, all future shuttle missions must be dedicated to the task, said John Grunsfeld, NASA's chief scientist.

"This was really a tough decision," Grunsfeld conceded. "It was very painful for everyone involved."

He said the loss of the space shuttle Columbia on Feb. 1 also played a significant role in the Hubble decision.

New safety protocols devised after the accident require astronauts to be capable of inspecting the exterior of the spacecraft for damage - such as the damaged wing tiles that caused Columbia's demise - and evacuating the shuttle if necessary.

Missions to the International Space Station meet both safety requirements.

Trips to the Hubble, isolated 350 miles above Earth, would not.

Grunsfeld said the new safety procedures would also require that a second shuttle be fueled and standing by if a Hubble-bound mission got into trouble - a requirement too expensive to fulfill.