Intel Corp. on Tuesday reported third-quarter profits that tumbled 77 percent as it struggled with slowing economies and weak personal computer sales, prompting it to forecast sluggish sales in the fourth quarter, typically the industry"s strongest. Intel INTC.O, the No. 1 chipmaker, said that net income before acquisition-related costs fell to $655 million, or 10 cents a share, from $2.89 billion, or 41 cents, a year ago, before 5 cents a share in acquisition-related costs. Sales fell 25 percent to $6.55 billion from $8.73 billion. The Santa Clara, California-based company had been forecast to report a per-share profit, excluding the costs, of 10 cents a share, within a range of 8 cents to 11 cents, according to Thomson Financial/First Call. Sales were forecast on average at $6.38 billion. Intel, which has been buffeted this year by weak demand and competitive pressure from rival Advanced Micro Devices Inc.