DETROIT — LIKE Dr. Seuss's Grinch, General Motors Corporation has stolen Christmas for tens of thousands of its workers.The nation's largest automaker announced sweeping cutbacks Dec. 18. But GM workers were not told which 21 factories and 74,000 jobs will disappear. And so, as GM's plants are closed for the holiday break, a lot of workers are sitting home still wondering how much longer they'll have a job. That word could take months. GM chairman Robert Stempel did not want to be a Grinch. "I would have preferred to do this in January, which was my original plan," he said. "A lot of people are scared down here," says Dave Perdue, president of United Autoworkers Union Local 276, representing GM's Arlington, Texas, assembly plant. It's one of two factories producing the Chevrolet Caprice and other full-sized sedans. The other is Willow Run in Ypsilanti, Mich. Sales of those so-called "B-body" vehicles are running barely half of capacity, and in one of his few specific comments Mr. Stempel said the plants will be consolidated. But no one is saying which plant will survive. And that may set off a hot battle between workers at the two plants to come up with packages of concessions that might improve productivity - and convince GM to spare their jobs. "We are not in the process of whipsawing," Stempel insisted when asked if GM purposely pitted the plants against each other. "I'm holding him to his word, says Bob Harlow, president of the Ypsilanti's plant's UAW Local. But while Mr. Harlow says he won't play a game of whipsawing, he concedes he is looking for ways to show GM how to improve productivity at his factory. In Arlington, employees have already voted for a work-week of four 10-hour days to cut overtime costs. And they may approve a three-shift operation that would potentially make the aging factory even more efficient. "I don't care if you call it whipsawing, we're doing whatever is in our power to help our membership," Mr. Perdue says. National union leaders are also under pressure. Stempel made it clear he would like to renegotiate GM's costly contract. So far, UAW officials have forcefully resisted, but "there will be considerable pressures" on the union to change that stand from workers who think it could save their jobs, says Harley Shaiken, a labor professor and former union analyst. Even local governments are getting into the act. Politicians from the Ypsilanti area are planning to meet with GM to see if they can come up with a package of cost-savings. That's understandable when you consider the impact a plant closing can have on a local community. Five years ago, GM shuttered an aging Cadillac line on the west side of Detroit. Today, the neighborhood is filled with abandoned luncheonettes, convenience stores, and shops. Hourly employees aren't the only ones facing a holiday of uncertainty. GM's salaried work force will be cut by 10 percent, or 9,000, next year, reducing the North American white-collar staff to 82,000. By the mid-1990s, the salaried staff will be trimmed to 71,000, half its 1985 size. The cuts were not unexpected. During the last recession in the early 1980s the other US carmakers, Ford Motor Company and Chrysler Corporation, sharply trimmed their salaried ranks. GM weathered that storm with little change, and today has a "staffing level that exceeds its needs since it carries a 35 percent market share rather than the 45 percent share it had a decade ago," says Maryann Keller, an auto analyst with Furman Selz. "My personal opinion is that this is something they need to do," concedes Kurt Krueger, an employee with GM's finance subsidiary, General Motors Acceptance Corporation. With little more than a year of seniority, Mr. Krueger says he is likely to be among the first let go, but "you can't be angry with the company. A change has to be made." Despite the cutbacks, Stempel took pains to note, "our safety net is still in place." Even if their plants close, union workers will continue receiving most of their pay and benefits under several protective programs, including a "job bank" negotiated just last year. And cuts in GM's salaried ranks will come through attrition - retirements and early buyouts - rather than layoffs. But those who then try to find new jobs may have trouble finding pay and benefits as generous as GM's. Stempel's tough words didn't do enough to encourage Wall Street. GM's stock continued to fall after the announcement. Many industry analysts worry the cuts won't go far enough to stem GM's losses in the key North American market. This year, those operations will go as much as $8 billion into the red.