A leak in a natural gas line caused the explosions last week that destroyed a rocket-propellant plant vital to the U.S. space shuttle and ICBM programs, killing two people and injuring more than 350, company officials said Thursday.

"A high-pressure gas line passing through the plant suffered a catastrophic leak that reduced the pressure in the line very substantially," said Fred Gibson Jr., chairman and chief executive of American Pacifica Corp., parent company of the destroyed plant, Pacific Engineering and Production Co. (PEPCON)."The massive leak is believed to have saturated the earth below the paved surfaces of the PEPCON plant, and to have ignited. . . . All of the subsequent destructive events were cause by the gas leak, the gas fire and the gas explosion," Gibson said.

The Pacific Engineering plant, one of two domestic sources of the chemical ammonium perchlorate, vital to production of solid fuel for America's space shuttle and intercontinental ballistic missiles, was destroyed May 4.

The explosions killed two company officials, injured more than 350 people and damaged more than 3,000 buildings in the Las Vegas valley, which was rocked with the force of a minor earthquake.

Clark County fire chief Roy Parrish declined comment on the company report.

"We have not completed our investigation," Parrish said. "The site is sealed and nobody but fire investigators and representatives of the Environmental Protection Agency have been allowed on the scene."

Officials of Southwest Gas Corp., suppliers of the natural gas line, had no immediate response to the allegation. Utility officials had discounted the gas leak theory in earlier statements and said the gas company was a victim of the disaster not the cause.

Gibson acknowledged that Pacific Engineering experts have not been allowed to conduct an on-site investigation because the scene remains under the control of the fire department.

He did not explain how American Pacific Corp. arrived at its conclusion regarding cause other than the reference to a drop in gas line pressure.

"Prior public statements issued by Southwest Gas to the effect that explosions of ammonium perchlorate preceded and caused the gas leak and subsequent mass explosion were mistaken, and are completely inconsistent with the dramatic reduction in presure in the gas line that has been established," Gibson said.

At the urging of Gov. Richard Bryan, officials at the nearby Kerr-McGee chemical plant, the only remaining domestic source of the chemical, agreed earlier Thursday to halt production pending a safety review.

"We understand that the safety inspection must be completed as soon as possible in the interest of public safety and the national defense," Bryan told a news conference. "But the safety of Nevada citizens comes first."

Kerr-McGee voluntarily closed last week because of the Pacific Engineering explosion, but resumed operations Tuesday without announcement, setting off a furor among local, state and federal officials.

"We have decided to close in order to coooperate with the governor and the city of Henderson," said Kerr-McGee lawyer Paul Hejmanowski. "We are thoroughly convinced this plant is safe but we have consented to voluntarily suspend ammonium perchlorate production."

Kerr McGee and Pacific Engineering are located 2 miles apart on the outskirts of Henderson.

Sarah Keegan, a spokeswoman for NASA in Washington, said the plants combined turned out 66 million pounds of ammonium perchlorate a year compared with the rest of the Western world's annual production of 9.1 million pounds.

"In terms of how long they (Kerr-McGee) can be shut down without causing us (the space shuttle) problems, I don't know," said Keegan. A Pentagon spokesman said it was premature to speculate on what impact a Kerr-McGee shutdown would have on military missile programs.

Ammonium perchlorate is an oxidizer used in solid rocket fuel that propels the space shuttle, MX and Midgetman ICBMs and the Titan 4 and Titan 34D heavy-lift space boosters.

Top ranking defense officials met this week in Washington to assess the impact of a reduction in ammonium perchlorate production.

Wayne Mehl, an aide to Sen. Harry Reid, D-Nev., said after a closed-door Air Force briefing in Washington:

"Unless the United States restores production very quickly the shortage of ammonium perchlorate will impact defense because the current planned requirements can not be met with current stockpiles. We don't have a surplus. There is not even enough to meet currently planned activities."