Tri Valley Growers, a San Ramon food cooperative that is suffering from big losses, said it has named two turnaround specialists to lead the company and has laid off about 10% of its salaried work force. Robert D. Cook, 68, was named chief executive, and Timothy Barron, 49, was named president. Thirty-five of the cooperative's 520 salaried workers were fired, and 17 open positions will not be filled, said spokesman Steve Swasey. On Aug. 6, the co-op, owned by more than 500 fruit and vegetable growers, said its chairman, James Cooley, and president and CEO, Joseph Famalette, had resigned. The changes followed an announcement that the cooperative would post a loss of $79 million for fiscal 1998, primarily because of write-downs of old inventory. Last spring, Tri Valley management said that a decision to raise prices of canned fruit, olives and processed tomato products had backfired, with the result that the co-op sacrificed market share and profit margin. The company's brands include S&W Fine Foods, Libby and Libby Lite Fruits, Oberti Olives, Redpack Tomatoes and many private labels.