The future of 3,000 jobs at the Hagerstown, Md., plant of Mack Trucks Inc. and the fate of Mack's Allentown, Pa., assembly plant remained in doubt as company executives reached their self-imposed deadline last night without making a public statement on their decisions.

"We are all still waiting," said Mack Vice President William McCullough, adding that Mack's chief executive, John B. Curcio, was preparing to announce the firm's plans.

Mack has demanded substantial wage and benefit cuts from the United Auto Workers union, threatening to eliminate jobs at the company's Hagerstown engine plant and to leave Pennsylvania to build its new assembly plant in an area where labor costs are lower than Mack's current $23-an-hour rate. Company sources have said the firm is studying North and South Carolina among possible sites.

The UAW on Thursday said it would not accept pay and benefit cuts, offering instead to save Mack an estimated $90 million annually through changes in production methods, work rules and automation. The union also said it would divert roughly $1 an hour of all workers' wages into a fund to build a new plant for Mack and to modernize the 25-year-old Hagerstown facility.