FRONT ROYAL, Va. (AP) _ NASA officials, fearing a delay in the shuttle program, are seeking to keep the agency's only manufacturer of rayon from closing after it suffered big losses stemming from the Challenger disaster.

NASA said Tuesday it was talking to Avtex Fibers-Front Royal Inc. to keep the supply of a rayon yarn used in shuttle rocket nozzles in production, while the Air Force identified three missiles that could be affected.

The company took NASA by surprise when it announced Monday that it would close the Front Royal plant on Thursday, idling 1,300 workers and cutting off the government's only supply of the rayon, said Jerry Berg, a spokesman at NASA's Marshall Space Flight Center in Huntsville, Ala.

''It will jeopardize the space program if we do not figure some way to get Avtex Fibers back on line by spring,'' said Jim Thomas, assistant to the solid rocket motor program manager at Marshall.

Avtex Chairman John N. Gregg said Monday that without Avtex's rayon, the shuttle program might be grounded for up to two years after one more launch.

But Berg said there was enough of the rayon on hand for ''the next several shuttle flights.'' NASA initially said the next 12 flights through May 1990 would be able to stay on schedule, but Berg revised the statement later in the day.

Rocky Raab, a spokesman for the maker of the shuttle motors, Morton Thiokol Inc., said it was too early to say what impact the closing could have.

The fibers manufactured by Avtex are woven into a cloth by other companies, Raab said. Two more layers of contractors that treat it to make it resistant to high heat.

Thiokol buys the finished product for use in the nozzles of its shuttle motors, Raab said.

John Kelly, an Avtex spokesman in New York, said he did not know of any talks between Avtex, based in Valley Forge, Pa., and the government that could keep the plant producing the rayon.

Gregg said he lost a large amount of money because of the Challenger disaster that idled the shuttle program for more than 2 1/2 years.

At Andrews Air Force Base, Md., a spokeswoman for Air Force Systems Command said officials had determined that at least one missile system, stage one of the small ICBM, used the rayon.

Two other systems, the MX intercontinental ballistic missile and the Titan satellite launcher, may also depend on the rayon, but officials had not determined that for certain by late Tuesday, Maj. Janis Bybee said.