RAF FAIRFORD England (Reuters) - The Pentagon on Thursday said key F-35 contractors Lockheed Martin Corp (>> Lockheed Martin Corporation), Northrop Grumman Corp (>> Northrop Grumman Corporation) and BAE Systems Plc (>> BAE Systems plc) would invest up to $170 million (99.35 million pounds) over the next two years to drive down the cost of the new warplane.

Under the plan, called the "Blueprint for Affordability", the contractors would recoup their investment and profit from the accrued savings only after the cost of the plane was reduced, the U.S. Department of Defense said in a statement.

It said the U.S. government could invest additional money from 2016 to 2018 if the initial cost reductions were successful, it said.

(Reporting by Andrea Shalal; editing by Jason Neely)