General Motors Corp. said yesterday it will begin a $200 million expansion and refurbishing program in its 45-year-old Baltimore car and truck assembly plant, ending months of specutlation about the future of one of the harbor city's major employers.

The plant on Broening Highway, which employs 4,000 workers, will be the 1980s. By the summer of 1982, only front-wheel-drive, fuel-efficient models will drive out of the new Broening Highway plant, General Motors officials said.

The renovatins will add 433,000 square feet of space to the 2.5-million-square-foot facility, GM officials said.

During a visit to Baltimore last Mar, GM President Elliott M. Estes said that the worldwide expenditures "will buy us not only a completely redesigned product lineup but also new and modernized production facilities. These new and upgraded facilities are as critical to our success as our brand new products.

"And since our new products will require all new tooling, it makes sense to built new plants or modernize old ones when the new machinery is installed," Estes said.

Earlier this year, GM Chairman Thomas Murphy aroused fears about the Baltimore plant's future when he suggested the possibility of building a new plant, possibly outside of the city.

The company decided to stay in Baltimore after intense lobbying from Baltimore's mayor, William Donald Schaefer, a GM spokesman said. "Schaefer was very involver and very instrumental," the spokeman said, adding that GM is "one of the largest industrial employers in the city."

However, the company laid off 2,300 workers earlier this year and has brought back only 400, the GM spokesman said. "Those were indefinite layoffs," he said, adding that he doesn't know if any more are planned.

The plant's manager, Walter J. Gregonis, said during a press conference in Baltimore that the company will try to maintain as much production and employment as possible during the remodeling.

For example, truck production will continue to the end of he 1981 model year and then that area will be remodeled as part of the passenger car assembly operations, Gregonis said. Passenger car assembly will continue into calendar 1982, he said.

"Because the plant will be one of the most modern, efficient automobile assembly plants in the world, we will want to keep it operating at the highest capacity possible," Bregonis said. "This means long-term, steady work for our employes located here."