Martin Marietta Corp. has laid off 115 employees at its Middle River, Md., plant as part of an overall restructuring of its work force that is likely to result in further layoffs at the plant in coming weeks.

The immediate cause of the layoffs is the winding down of two longtime programs: production of B1 bomber tail sections and Patriot missile canisters. The cutbacks have been anticipated for some time, a company spokesman said.

About 4,400 workers are employed at the Middle River plant, which is 12 miles east of Baltimore.

The Patriot missile contract, which Martin Marietta lost last year to an Israeli company, will finish at the end of March. At that time, some of the 70 workers left on the production line may be let go while others will be shifted into other jobs, spokesman Buzz Bartlett said. "There may be some further layoffs, but it's hard to tell," he said.

The 58-year-old Middle River facility is the home of the Martin Marietta Aero & Naval Systems, a division of Bethesda-based Martin Marietta Corp. It has long been known as a production plant -- it built the famed B26 "Martin Maruader" bombers in World War II -- but in recent years has been aggressively seeking to target more high-tech weapons development contracts, particularly in the area of antisubmarine warfare.

As a result, said Bartlett, the plant this year will probably be hiring more engineers -- 200 -- than the mostly production workers it expects to be laying off.

"This company is going through a transition -- from primarily production to primarily development," said Bartlett. "The larger strategy is to invest our resources in development, assembly and test-type contracts as opposed to strictly production."

One year from now, he said, the plant will probably have the same size work force it has now, although the mix will be markedly different.

The B1 bomber tail sections, which the company built for prime contractor Rockwell International, has brought the Middle River facility about $270 million worth of business since 1982. There were about 350 workers on the program at its peak, but with the recent end of B1 production, Martin Marietta began laying off those workers at the end of January. Bartlett said some of the workers have been shifted to other jobs at the facility, while "we've managed to place 30 in new jobs outside the company."

The Patriot missile contract, which has brought the company about $20 million over the past eight years, was lost last year to an Israeli company called IMI, Bartlett said. He noted that the job represented less than 10 percent of the plant's existing revenue.