A design flaw in a mirror developed for the next generation of advanced weather satellites could delay their launch and leave forecasters at least temporarily reliant on slower, less detailed technology to track threatening weather, government officials said yesterday.

The $100,000 mirror is being built for the new series of Geostationary Operational Environmental Satellites (GOES) designed by NASA for the National Weather Service, to orbit 22,300 miles above Earth. The problem is not comparable to or related to a major flaw found recently in the Hubble Space Telescope, according to officials of both agencies. Word of the weather satellites' flaw was first reported by the New York Times.

The GOES satellites provide the continuous overviews of weather across the Western Hemisphere seen routinely on weather maps on the nightly television news.

Only one such satellite is in orbit. Officials of both NASA and the National Oceanographic and Atmospheric Administration, which includes the National Weather Service, expressed some concern that it could fail before a replacement is lofted. But they said that possibility seems remote.

"There is a 90 percent probability of no failure through late 1992," said Elbert W. Friday Jr., head of the National Weather Service. By then, he said, he expects the first of the replacement satellites -- known as GOES-NEXT -- to be ready.

If it isn't, he said, the agency has a contingency plan to use other satellites, radar and specially equipped tracking planes to provide weather forecasting and storm tracking data. But he emphasized that the fallback system would be less capable than GOES.

"GOES clearly is not the only tool, but with respect to tracking storms it's our best tool," he said, "Without it, you would see a jerky, incomplete motion" in the weather pictures, which would take longer to assemble, and would reduce forecasters' ability to predict hurricane movements.

Officials said repairing the flaw could delay completion of the instruments for two to six months but precise estimates of the cost, and the length of delay, must wait until at least late next month, when a special NASA-contractor team is expected to recommend a solution.

James R. Greaves, NASA's manager of meteorological satellites, said the new satellites are designed to remain in a stable position in space, focused on Earth like spy satellites, instead of spinning like the earlier satellites in the GOES series.

Initial tests seemed to show the satellites' mirror, which measures 20 by 13 inches, "would meet specifications," he said. But in late 1989, the first indications of a problem prompted the Aerospace-Communications Division of ITT Corp., designer of the mirror and a subcontractor to Ford Aerospace on the $900 million project, to devise a more rigorous test. That test, completed recently, showed that the mirror will be warped in an unacceptable way by heating from sunlight.

A Senate Commerce, Science and Transportation Committee staff aide said, "There's been a great deal of concern on the committee for a long while that the GOES program was behind schedule and over budget."

The aide attributed this to a combination of factors, including the loss of one GOES satellite when its Delta booster failed, the fact that GOES-NEXT is an attempt to "push new technology," and "severe constraints" in the NOAA budget for most of the last decade.