A drop in maintenance and modernization work will result in hundreds of layoffs at submarine manufacturer Electric Boat this year, although new hires will leave the work force numbers unchanged, officials said Tuesday.

Executives of Electric Boat, a subsidiary of General Dynamics Corp., said at a meeting outlining business objectives for 2010 that between 400 and 600 layoffs are possible in addition to 100 to 200 furloughs, spokesman Robert Hamilton said. So-called waterfront workers, those who do carpentry and other trades, will be primarily affected, he said.

The shipyards in eastern Connecticut and Rhode Island employ about 10,700 workers.

Much of the reduction in work is due to a drop-off in maintenance and modernization. Electric boat did 360,000 hours of work for naval shipyards in 2008, and the number fell to 100,000 hours last year, Hamilton said. The company expects "very little of that work this year," he said.

President John P. Casey told state legislators at the briefing that Electric Boat will need to hire 300 to 400 engineers and designers to work on researching and developing the next-generation ballistic-missile program and continue work on a surface ship program run by its shipbuilding partner, Northrop Grumman Newport News in Virginia, The Day of New London reported.

"Our engineering business looks so robust, we will probably not have the facilities we need to accommodate the engineering staff," Casey said.

Electric Boat will likely rehire construction trade workers, and as a result, the company expects the work force to be level and increase in 2011, Hamilton said.

Congress has appropriated $500 million for the Ohio submarine replacement program. Construction will not begin until 2019, but design work is "very significant," Hamilton said.

In late 2008, Electric Boat, a subsidiary of General Dynamics, and Northrop Grumman Corp. won a $14 billion contract to double submarine production to two annually.

Electric Boat has shipyards in Groton, Conn., and North Kingstown, R.I.