NASA has developed a $40 million plan to fix the Hubble Space Telescope by replacing one instrument on the orbiting outpost and sacrificing another to make room for a corrective device, officials said.

The repairs, which would be conducted during a spacewalk by shuttle astronauts in 1993, should restore the telescope to at least 90 percent of its intended capacity, David Pine, deputy program manager, said Wednesday."The telescope today is the best optical telescope - by far the best ultraviolet telescope - in the world, even with the problems. Having the opportunity to bring it back to its original pre-launch expectations is certainly very pleasing to everybody," Pine said. "It's looking really good."

The plan was submitted to top NASA officials this week as part of planning the agency's budget and a decision on whether to proceed was expected by April, Pine said.

The $1.5 billion telescope was expected to revolutionize humanity's understanding of the universe by using a highly advanced optical system to peer deep into the cosmos from its perch high above Earth's atmosphere.

But about two months after the long-awaited telescope was placed into orbit in April, scientists were shocked to discover the instrument's supposedly perfect primary mirror was shaped incorrectly, preventing the telescope from focusing properly.

Although the telescope has proved able to conduct valuable research in its current condition, NASA has been studying various options for correcting the defect, called spherical aberration.