Tooele County deputy sheriffs are on duty at the entrance of Amax Magnesium on the west side of the Great Salt Lake in the wake of rock- throwing incidents in connection with a strike against the company by 225 members of United Steelworkers of American, Local 8319.

Sheriff Donald Proctor said he would keep between one and three deputies at the scene, depending on the number of picketers who show up, to prevent further rock-throwing that has left two supervivisers injured and several vehicles damaged.Lee Brown, vice president of human resources and public and government affairs, said the strike started Saturday at 6:30 p.m. and since that time supervisory personnel have kept the plant open to continue the magnesium production.

"The company intends to operate the plant during the strike action and encourages the employees to return to work," Brown said in a prepared statement.

The local had a three-year contract with Amax that expired March 19. Since then, the employees have been working without a contract in anticipation of negotiations leading to a new contract.

However, Don Collard, staff representative for the union, said negotiations broke down and the members voted to strike.

"This strike was initiated in spite of major increases in pension benefits, other benefits and the introduction of a new incentive pay program," Brown's statement said.

Under the new incentive pay program, he said, employees' base wages were reduced 5 percent, but quarterly incentive wage bonuses could be earned at 7.5 percent of quarterly wages the first year; 8.76 percent the second year and 10 percent the third year.

The company considers it the best United Steelworkers contract in Utah.

Union officials disagree. Collard said the union made wage concessions in the last contract and won't make more concessions.

He said the company also wants to reduce the 12-hour day to 11 1/2 hours with an unpaid 30-minute lunch hour, and the union also wants the same health insurance plan as the salaried employees.