The Reagan administration's insistence on "privatization" of government programs wherever possible may delay the start of production of the Advanced Solid Rocket Motor and thus keep Utah's Morton Thiokol Corp. in the shuttle booster business longer than planned.

James Fletcher, head of the National Aeronautics and Space Administration, told reporters Monday that the White House cut from the budget $60 million to begin building a NASA-owned advanced booster plant in Mississippi. The reason he gave was that the president's Office of Management and Budget objected to having the government replace private-industry ownership of such an industrial operation.Rocky Raab, who manages external affairs for Morton Thiokol, said Fletcher's announcement reaffirms the position Thiokol officials have always maintained - that "the space business is one of private industry and should not be a government-owned proposition."

Because Morton Thiokol will be building the redesigned solid rocket motors until the Advanced Solid Rocket Motor plant is completed, any substantial delay or cancellation of the program "would mean that Morton Thiokol will build the rocket motors indefinitely," said Raab.

"As it stand now, we'll be building rocket motors through 1997.

"We've proved we can build the safest, most reliable solid rocket motors in the world and we've pledged to continue that performance."

Thiokol has said it would not bid on producing the new motor, after its part in the shuttle disaster three years ago.

NASA still wants a government-owned, contractor-operated plant. To resolve the question, a Source Evaluation Board is looking at both options.

Plans had been for the motor to power shuttle launches after 1992, but unless the present standoff is solved it could be longer. Meanwhile the Thiokol plant at Brigham City remains the only U.S. shuttle booster producer. With nine shuttle launches planned for 1990 and possibly more in future years, the delay could mean orders for from eight to 10 additional booster motors from Brigham City.