Plagued by the prolonged economic slump and falling semiconductor prices worldwide, electronics giants Toshiba Corp. and Hitachi Ltd. on Tuesday reported their first midterm net losses in decades.And they were huge. Hitachi Ltd. posted an unconsolidated net loss of 124.7 billion yen -- the first midterm loss since fiscal 1950, company officials said. Meanwhile, Toshiba Corp. realized an unconsolidated net loss of 6.4 billion yen for the April-September period, marking the first time the firm has slipped into the red in 48 years, company officials said.All four of Toshiba's main business segments saw a decline in sales, which included information and communications systems sales falling by 11 percent, electronic devices and materials by 14 percent, power and industrial systems by 16 percent and consumer products by 6 percent. Total net sales dropped 12 percent to 1.6 trillion yen.For the full fiscal year, however, Toshiba predicted a net profit of 12 billion yen on increased sales of personal computers and stabilized prices of semiconductor memories in the remaining six-month period.In sharp contrast, Hitachi predicted 260 billion yen in net losses for all of fiscal 1998 on an unconsolidated basis. If realized, it would be the first red-ink earnings report for a business year since Hitachi's establishment in 1920, except for the period of economic confusion immediately after World War II, company officials said.Yoshiki Yagi, senior executive managing director at Hitachi, said that the firm's performance in computer display and liquid crystal business were particularly poor relative to expectations.JAS suffers 237 million yen net lossJapan Air System Co. reported 237 million yen in net losses for the first half of fiscal 1998 on an unconsolidated basis after incurring 2.7 billion yen in losses due to a revaluation of its securities holdings, the carrier announced Tuesday.During the April-September period, JAS secured 171.4 billion yen in sales, up 1.0 percent from the same period in the previous year, and posted 2.5 billion yen in pretax profits.A reappraisal of the carrier's stock holdings reduced their value by about 20 percent, reflecting the stagnant stock market, JAS officials said. JAS expects the business environment to become more severe in the second half of the current business year amid the downward trend in air fares, the officials added.Domestic air fares dropped an average 2.4 percent from the same period in the previous year, they said. Accordingly, the carrier lowered its previous forecast for unconsolidated sales to 329.6 billion yen, down 1.3 percent, for the full business year that will end next March. JAS now expects 2.8 billion yen in unconsolidated net losses for the period.