Hercules Inc. will announce the results this week of its investigation of a fire that caused an estimated $15 million in damage to a building where rocket fuel is mixed, an official said.

Company spokesman Jack DeMann said the outcome of the probe will determine whether work resumes immediately at an identical fuel-mixing facility.Unfavorable results could cause work at the second plant to be delayed as long as two more months, DeMann said.

DeMann said production at the undamaged building was stopped as a precaution after the March 29 fire.

"This is a very unforgiving process," DeMann said. "We simply shut the other one down until we could find out what happened. You just don't want to take any chances."

The fire burned 25,000 pounds of fuel for the Delta II rocket booster. No one was injured.

Hercules has since not made the booster fuel or propellant for boosters, which will propel the new Trident 2 submarine-launched nuclear missile.

The Navy said the fire investigation is one of three things delaying sea-launch tests and deployment of the new multiple-warhead Trident 2. Deployment now is expected in March 1990.

The other factors delaying the Trident 2 are a strike at a California company making second- and third-stage rocket nozzles and redesigns of first-stage motor parts, including the nozzle made by Morton Thiokol, after failure of the first sea launch March 21.

The Navy said 15 of 19 land launches of the Trident 2 have been successful.

Hercules is undecided on whether to fix the fire-damaged building or erect a new facility, DeMann said. The company is working with local governments to get permits needed to start.

A third mix building is under construction and is expected to be ready before year's end, he said.