LOS ANGELES (AP) - Insurance companies could wind up the big losers in the worry over Year 2000 computer glitches, whether or not the millennium bug actually strikes Jan 1. In recent weeks, four companies and two local government agencies have filed multimillion-dollar lawsuits against their insurers to recoup the cost of upgrading computer systems. Others are waiting in the wings with claims, attorneys say. Xerox Corp. has sued its insurer for $150 million in Y2K remediation costs. Nike is seeking reimbursement of an estimated $110 million layout for Y2K preparations. Others that have sued are Unisys Corp., GTE Corp., the Port of Seattle and the Royal Oak, Mich. School District. The lawsuits, filed since July, altogether seek about $700 million from insurers.