Utahns like to joke that when the big earthquake hits and California slides into the sea, they'll be instant owners of beach-front property.

But it's no joke that barring such an improbable geologic scenario, the chances of Utah and Morton Thiokol remaining part of America's space shuttle program into the next century appear rather slim at the moment.Two-time NASA Administrator James C. Fletcher said Wednesday night that the need to be able to transport the next generation of the shuttle's solid rocket motors by water is the compelling reason behind the space agency's plans to build a new manufacturing facility along the Gulf Coast.

Translation: Utah's landlocked geography won't be a big selling point.

But Fletcher, speaking at the Weldon J. Taylor Executive Lecture Series at Westminster College, hastened to add that no decision on the site for the new rocket manufacturing facility has been made despite comments made to Congress recently by high-ranking NASA officials indicating otherwise.

Fletcher, who earlier headed NASA from 1971 to 1977 before returning to the job again in 1986 in the wake of the Challenger disaster, said Rear Adm. Richard Truly, associate administrator for spaceflight, spoke for many inside NASA when he said the larger boosters probably won't be built at Morton Thiokol. But Fletcher is still the one making the decisions.

He denied talk that moving the shuttle program out of Utah is meant to punish Morton Thiokol for its role in the Challenger tragedy.

"We absolutely aren't trying to punish Morton Thiokol," Fletcher said. "They did a super job in making (shuttle) motors in the first place and have done even more for the (post-Challenger) recovery."

He said it's a misnomer to suggest NASA's proposed facility would duplicate existing facilities at Morton Thiokol's remote Wasatch Operations, 25 miles west of Brigham City. "It's not possible to build what NASA wants at Morton Thiokol. What we're talking about would require new technology and a new plant."

Fletcher said the aerospace industry still has a long way to go in understanding solid rocket motor technology. As it stands now, rocket motors are "little more than rubber, glue and putty," and no one is completely sure why they work the way they do, he said. A new state-of-the-art facility would permit much higher quality control and help rocket motor production evolve into a science from its current art-form status.

He said reports of a $1 billion price tag to the taxpayer to build this new manufacturing plant are misleading because that figure includes movable equipment. The actual cost for constructing the facility alone is closer to $300 million. Plus, the likelihood is increasing that the facility won't be constructed by the taxpayer at all but rather will be built by a private contractor who will recoup that investment over the next 20 or 30 years by supplying hardware for shuttle flights.

Fletcher also hinted he might not be ready to leave the space agency for the second time, as has been widely reported, when President Reagan leaves office next year. "Who knows," he said, "I may still be there."