Citing concerns about the safety of nearby residents, Salt Lake County planners rejected plans Tuesday for Hercules Inc. to expand so it can build Titan IV and Delta II missiles.

Company officials, who had hoped to begin construction on the $145 million expansion by June 1, said they will appeal the decision to the County Commission. It is unlikely the commission will hear the matter before June 1.If commissioners reject the expansion, the company will lose $2 billion over the next 10 years, and the local economy may suffer a loss five times that, said Jack DeMann, Hercules public affairs director.

"If we eventually get a favorable decision, the frustrations will have been minimal," DeMann said, adding he could not answer the question of what company officials would do if the commission rejects the expansion.

The County Planning Commission, whose members are appointed by the County Commission, took more than two months to decide on the expansion, holding several hearings and studying data. The final result was a tie vote, 2-2, with Commissioner Henry Hance abstaining because of a possible business conflict. Tie votes count as rejection of a motion.

The company's plans may have suffered most from an unrelated accidental explosion in Henderson, Nev., earlier this month. Critics questioned what a similar accident would do to nearby residents in the unincorporated Magna area.

Hercules officials felt they had provided evidence that a similar accident could not occur at their rocket manufacturing plant. But two commissioners and many local residents disagreed.

"The economic well-being of this valley should not be based on a missile industry," said Commissioner James Smith of Magna, explaining why he voted against the expansion.

Commissioner Madelyn Player also rejected the plans, comparing the risk of an accident to that of similar accidents that have occurred elsewhere in recent years.

But Commission Chairman Chandler St. John said he is satisfied the plant would pose no danger to nearby residents.

"I felt that the serious concerns were well answered," he said. "We hired outside consultants and got opinions from everyone we could think of asking."

Commissioner Richard McNeil agreed. "We've gotten into a panic situation because of an unfortunate incident in Nevada," he said.

In an indirect way, company officials may have caused their own problems by threatening to leave Utah last year unless the county stopped developers from building houses close to the plant. The threat of an accidental explosion was raising the company's insurance rates, they said, maintaining that houses should not be built within a 1.5-mile buffer zone around the plant.

Now, critics claim the expansion would push the buffer zone out farther. Hercules officials denied those claims, saying they were using pits and other construction methods to limit the effects of a blast.

County officials signed an agreement with West Valley City last year after Hercules threatened to leave the state. The agreement called for West Valley City to annex half of Hercules and to buy $10 million worth of undeveloped land in the danger zone. Hercules also agreed to buy about $8 million worth of land.

Magna residents tried unsuccessfully to stop the annexation.

The expansion is planned for the unincorporated county and would make up for some of the tax money the county lost when West Valley City annexed half the plant, company officials said.