The cost of developing the F-35 Joint Strike Fighter rose 4.3 percent to $395.7 billion last year and the plane will not reach full-rate production until 2019, the Pentagon said.

The new schedule is two years later than planned.

Pentagon cited a slowdown in orders from the US military and other countries as a reason for the higher cost of the Lockheed Martin Corp next-generation combat plane, which has been dogged by delays and cost overruns.

The Pentagon's acting chief weapons buyer Frank Kendall approved continued low-rate production of the supersonic, single-engine fighter, according to an acquisition memorandum dated March 28.

New projections by the Pentagon also show that the total lifetime cost of the new warplane, including development, production, operating and maintenance costs, and inflation, will reach $1.51 trillion over the next 55 years.

The new estimate compares with a previous one of about $1.38 trillion over the life of the program, but adds three years to the equation, from 2062 to 2065, at the highest inflation rate, and uses 2012 as a baseline rather than 2002.

Operating and support costs alone are now expected to reach about $1.1 trillion, up from last year's estimate of $1 trillion, according to a Pentagon report to Congress.

Lockheed is developing three variants of the new plane for the US military and eight partner countries - Britain, Canada, Australia, Italy, Turkey, Denmark, Norway and the Netherlands.

The partners now plan to buy a combined total of 697 planes, down from 730 in the previous Pentagon estimate.

Japan, one of the first foreign customers outside the partnership, said in late February it might cancel orders for 42 F-35 fighters if the price goes up or deliveries are delayed, prompting Vice Admiral David Venlet, who heads the program, to say he had assured Japan that its deal would not be invalidated. - Reuters