In what could be a reprieve for 5,500 workers at Boeing Co.’s Long Beach C-17 plant, funding for seven additional C-17 military transport planes has been included in the latest defense appropriations bill, U.S. Senator Dianne Feinstein announced Thursday.

The funding is contained in the House-Senate Conference Committee bill, an attempt to iron out differences in military spending bills passed by the House and Senate. It comes on top of funding for three C-17 aircraft contained in a $50 billion “bridge fund” for combat operations in Afghanistan and Iraq, and 12 additional C-17 aircraft ordered by the military.

Last month, Boeing had announced it would close its Long Beach plant in early 2009 unless additional funding came through. The C-17 has been the target of Pentagon budget cutters given its $200 million cost to produce. If this latest funding survives the legislative process, it could keep the Long Beach plant open through the remainder of 2009.

The decision follows by just one day the release of a report by the Government Accountability Office that criticized a Pentagon study that formed one of the bases for the military’s decision to cut the C-17 program.

The GAO report on the Mobility Capabilities Study intended to be a comprehensive review of the military’s transportation needs didn’t address specific findings but did conclude some of the results were “incomplete, unclear or contingent on further study.”

Boeing officials could not be reached for comment late Thursday afternoon.