Apparent defects in a key mirror aboard the crippled Hubble Space Telescope would have been detected before launch if NASA had used Defense Department facilities for testing spy satellites whose design resembles the Hubble, according to knowledgeable industry officials and space scientists.

The National Aeronautics and Space Administration never ordered such tests, despite a routine government practice of ground-testing top-secret fully-assembled KH-9, or Hexagon, military spy satellites deployed over a 15-year period, the officials said.

The spy satellites are telescopes like the Hubble that look down at Earth instead of out into space.

The officials, including several with experience in military and civilian space programs, asserted that equipment needed to conduct such tests was readily available to NASA, although it would have required some adjustment to accommodate the more-sophisticated space telescope design.

However, a senior NASA official, Charles O. Jones, said yesterday that he was not aware of any facilities used by the military to test spy satellites and that no such facility was offered or discussed with him.

Jones, a deputy chief of guidance, control and optical systems at NASA's Marshall Space Flight Center in Huntsville, Ala., was involved with design of the Hubble mirrors over a decade ago and remains with the program.

"We are rather astounded at this error," Jones said of the mirror flaw, because the space agency believed rigorous but separate tests of the telescope's two mirrors would catch any major flaws.

Jones said testing the telescope as a single fully-assembled element at a specially designed facility would have been "difficult, costly and appeared unnecessary."

But two independent space scientists, who asked not to be identified, disputed the space agency's statement that obtaining proper test equipment would have cost hundreds of millions of dollars and delayed the telescope's development. They said existing testing equipment could have detected a gross technical flaw of the type now suspected in one of the telescope mirrors at a cost of only a few million dollars.

"The military's {testing} setup would have detected an error that large," said an independent scientist with knowledge of the Hubble telescope and the KH-9 photo-reconnaissance program. Each of the roughly 20 KH-9 spy satellites launched from 1971 to 1984 used mirrors produced by Perkin-Elmer Corp., the Danbury, Conn., firm that made the Hubble mirrors, several officials said.

The independent scientist said NASA selected Perkin-Elmer, without seeking competitive bids from other firms because of the company's extensive experience with the KH-9 program, a factor he said that should have made NASA officials aware of the routine testing practices. He said the Hubble project was completed in 1981 as the KH-9 production program was winding down, and that no subsequently manufactured spy satellites have a similar design.

The Hubble Space Telescope, designed to peer at distant stars, was a more sophisticated variant of the KH-9 satellites used to observe the Soviet Union from orbits more than 100 miles above the Earth. One official said the Hubble was designed to meet specifications three to four times more stringent than those for the KH-9, a goal that the space agency is now viewed as having missed by a wide margin.

The Hubble telescope's large 94.5-inch primary mirror gathers and concentrates starlight, reflecting it onto a smaller 12-inch secondary mirror that further concentrates the image and focuses it on a tiny spot, the equivalent of the place where film would be in a camera.

According to NASA and officials at Hughes Danbury Optical Systems, Perkin-Elmer's new name after a takeover, the primary and secondary mirrors were tested individually, but were never mounted together as they are in the Hubble and tested in tandem.

Even as the mirrors were being built a decade ago, NASA scientists were saying that a true test of the Hubble mirrors was too costly. "The technical feasibility of testing so large a system . . . was given serious consideration but the associated costs were untenable," Jones wrote in 1979. The implication of such a "testing philosophy" was that the final alignment of the telescope would be performed in orbit, he wrote.

The decision not to test the mirrors together was "justifiable at the time, because {the project's} ability to measure was certainly adequate to catch manufacturing flaws," said Al Boggess, projects scientist for the Hubble program at Goddard Space Flight Center in Greenbelt. "These are always difficult matters of judgment. Clearly somebody called it wrong."

Lennard Fisk, head of NASA's science office, told the Senate Commerce, Science and Transportation subcommittee on science, technology and space yesterday that testing the mirrors together "was judged not to have a good cost-to-benefit ratio."

Sen. Albert Gore Jr. (D-Tenn), chairman of the subcommittee, charged that NASA managers had diverted funds and manpower from the Hubble program to support other projects. Gore said that when Hubble was being built, NASA was reducing personnel charged with quality control.

Fisk countered that while previous Hubble management "was unnecessarily complex," the Hubble program did not suffer for a lack of funding. He said the Hubble program paid for huge cost overruns, escalating the price tag from $450 million in 1978 to $1.6 billion when it was launched two months ago.

Two other Hubble project scientists at the Marshall center, Fred Wojtalik and John Humphreys, emphasized that to the best of their knowledge, no military facilities would have been adequate to test the telescope's ability to meet full design requirements.

But a third independent scientist said the military facility could have been used to find "a major goof, even if it would not find the finest error."

NASA and industry officials who worked on the Hubble say a detailed chronology of the agency's decision-making would take months to develop.

Staff writer Kathy Sawyer contributed to this report.