ECONOMY Car and light-truck sales by the nation's Big Three automakers skidded 20.6 percent in mid-December, the companies said. Car sales dropped 18.9 percent and truck sales were off 22.8 percent. Through Dec. 20, they sold cars and trucks at an average daily rate of 31,333, down 6.9 percent from the same period in 1989.

COMPANIES MNC Financial's preferred stock and long-term debt ratings were lowered by Standard & Poor's and Moody's Investors Service. Both services cited MNC's decision to suspend payment of its stock dividend. Moody's also said it expected "MNC's asset quality will continue to deteriorate, primarily because of its significant exposure to its weakening local real estate markets." American Airlines, which suffered disrupted service during the holidays, apologized to passengers in full-page newspaper advertisements blaming the carrier's pilots union. The pilot's union denied it has been hampering airline operations. Between Saturday and Monday, more than 1,000 flights were canceled. Zapata Corp., an energy and fishing concern founded nearly three decades ago by President Bush, avoided a bankruptcy filing by successfully buying back a series of debt securities at a steep discount. AT&T increased the long-distance price cuts it announced last month from $34 million to $83 million, channeling into additional price reductions money the federal government had previously told it to put into a fund that subsidizes certain phone service. The new cuts, in effect since Tuesday, bring prices down by an average 1 percent. Rupert Murdoch's bankers might complete a multibillion-dollar debt restructuring agreement for News Corp. next week. News Corp., which in the United States owns the Twentieth Century-Fox film studio, Fox Broadcasting Network, newspapers, book publishing operations and magazines including TV Guide, would reportedly dispose of up to $2 billion in assets over the next three years in an effort to service its rescheduled debt, bankers said. Amoco said it has made its seventh significant natural gas discovery -- 10.9 million cubic feet -- in the past 24 months in the Oklahoma portion of the Arkoma Basin. Hills Department Stores will close 28 of its 214 stores as part of a restructuring program. The Canton, Mass.-based company said the 28 stores, many of which were acquired from the Gold Circle division of Federated Department Stores, are in Ohio, Tennessee, Michigan, New York, Georgia, Illinois and Indiana, and some 3,125 employees will lose their jobs.

INTERNATIONAL Japanese businessmen see Japan's four-year-old economic expansion ending sometime in 1991, according to a survey of chief executives of 100 major companies published by Kyodo News Service. German currency speculators and communist-run businesses cost the government $666 million by manipulating aspects of German unification, an official said. Officials have identified 54 specific cases where people managed to make vast amounts of money off the economic merger of the German nations, but said it will take at least six months to sift through evidence needed to bring criminal charges.

CONTRACTS The University of Texas received a $186.3 million Navy contract for undersea weapons research. GE won a $58.4 million Navy contract for cruiser weapons systems. Westinghouse Electric won a $32.5 million Air Force contract for surveillance radar.

PEOPLE Lawrence Lindsey, a 36-year-old White House aide and economist, is among the candidates to fill a vacancy on the Federal Reserve, Bush spokesman Marlin Fitzwater confirmed. Lindsey has been working on the administration's proposals to overhaul federal laws governing banks and the deposit insurance system.