The U.S. military is looking to cut back on F-35 jet fighter purchases in its largest, but increasingly delayed aviation program, whose rising costs have received Congressional scrutiny.

The U.S. Department of Defense will propose to lawmakers to cut back on purchases of F-35 fighter planes plans in the next few years.

It will order 325 of the Lockheed Martin produced jets between 2012 and 2016, according to a published report. That is 124 fewer than anticipated last year.

The cuts in the Joint Strike Fighter program - which is funded by the U.S. and other friendly governments - will come despite an overall increase in the Department's budget over the next five years.

One version of the jet - to be used by the Marine Corps for short takeoffs and vertical landings - was being put on the equivalent of a two-year probation, Defense Secretary Robert Gates told reporters on Monday.

If we cannot fix this variant during this time frame and get it back on track in terms of performance, cost and schedule, then I believe it should be cancelled, he said.

He said the Marine Corps made a compelling case to get more time to fix problems.

Gates said that the Department of the Navy would buy more F-18 fighters and extend the life of 150 of those aircraft as a hedge against more delays in the JSF program.

He said Air Force and Navy's carrier-based versions were proceeding satisfactorily.

In March of 2010, the Government Accountability Office said, in the long term, the program would cost $323 billion to develop and procure 2,457 aircraft. GAO said at the time the program continues to struggle with increased costs and slowed progress.

Program acquisition costs had grown by $46 billion and development extended two and a half years since the program was initially approved in 2007.

Gates said the next five years will see a decline in the rate of growth of the Department's budget.

Government accountability office