The parent company of PEPCON Production, which is building a new rocket fuel plant in southwestern Utah, says it will sue Southwest Gas Corp. over the explosion that destroyed the old plant in Nevada.

Fred D. Gibson Jr., chairman and president of American Pacific Corp., said in a prepared statement Tuesday that it believes the gas company is primarily responsible for the fire and explosion May 4 that destroyed the ammonium perchlorate plant in Henderson, Nev.Ammonium perchlorate provides the oxygen in many solid-fuel rockets, including the space shuttle booster rockets and many military missiles.

Gibson said lawyers plan to file documents before Jan. 15 seeking recovery of the cost of damage in excess of the amount paid by insurance. He said the damage estimate exceeds $30 million.

Gibson did not say how much more in damages will be sought nor how much will be covered by the company's insurance.

Southwest Gas owns and operates a 16-inch, high-pressure natural-gas line that served the plant.

Regarding PEPCON's plant in Iron County, Utah, Gibson said the engineer-contractor hired in July has finished about 45 percent of the engineering and about 30 percent of the procurement.

Construction of the $50 million-plus plant, which began in October, is approximately 10 percent complete, he said.

American Pacific on Tuesday reported a net loss of $182,000, or 6 cents per common share, on revenues of $500,000 for the fourth quarter ended Sept. 30.

That compares with net earnings of $692,000, or 20 cents per common share, on revenue of $4.5 million for the same time last year.

For the just completed fiscal year, American Pacific reported net earnings of $2.7 million, or 58 cents per common share, on revenues of $12 million. That compares to with net earnings of $1.1 million, or 30 cents per common share, on revenues of $15.8 million for fiscal 1987.

Gibson said any comparison of revenues and earnings with the 1987 period should take into account that operations the last five months of fiscal 1988 after the May 4 fire and explosion in Nevada reflected primarily start-up activities. He said cash flows are attributable primarily to insurance settlements.