If a NASA advisory group had its way, Morton Thiokol in Utah would make space shuttle boosters for a long time - and may never have them replaced with planned advanced boosters.

The Aerospace Safety Advisory Panel said Tuesday that Morton Thiokol's boosters are less costly and likely more safe than the planned advanced boosters - which could take years and billions of dollars to achieve the reliability of the current redesigned rockets.So the panel urged NASA Administrator James C. Fletcher to halt plans - at least temporarily - for a new advanced-booster factory in Yellow Creek, Miss., to replace boosters now built in Utah.

NASA officials have said they are taking the advisory panel's suggestion seriously but that top NASA officials still feel the new advanced boosters are needed.

NASA planned to announce sometime next month a contract to produce the new boosters. Hercules Inc. of Magna is on one of two teams bidding.

But Morton Thiokol chose not to bid and instead to concentrate its efforts on redesigning the current boosters. It therefore faced leaving the booster business by the early 1990s.

In its report, the panel - which was first formed by Congress after the 1967 Apollo 1 fire that killed three astronauts - questioned "the wisdom of proceeding with the procurement of a new solid rocket motor which, by the time it is introduced, will have less proven and documented safety and reliability features than the current redesigned solid rocket otor."

It explained, "NASA's decision to procure the advanced solid rocket motor (ASRM) is based on the premise that the new motor will benefit from advanced solid rocket motor technology and new manufacturing methods and thus would evolve into a safer and more reliable motor."

But it said, "On the basis of safety and reliability alone, it is questionable whether the ASRM would be superior to the (current booster), which has undergone extensive design changes, until the ASRM has a similar background of testing and flight experience.

"This may take as long as 10 years from go-ahead. . . . Furthermore, it is not evident why the new manufacturing processes planned for the ASRM cannot be applied to the manufacture and assembly ' of the current boosters.

The panel recommended `that NASA review its decision and postpone any action until other alternatives have been evaluated."