Leading industry analyst Loren Thompson said on Wednesday that the programme could be ended after producing only 160 of the 277 planned aircraft.
He said the proposed cuts reflected "the convergence of severe budgetary pressures imposed by the Iraq war with some long-standing preferences among senior policymakers for less emphasis on conventional weapons programmes".
The US air force estimated the total of 277 planes would run to about $72 billion, making it the most expensive fighter jet in history.
The aircraft, known as the Raptor, is due to enter service in December 2005.
But Dennis Boxx, a spokesman for the plane's manufacturer and the nation's largest military contractor, Lockheed Martin, said the company had not been notified of any changes.
And defence department spokesman Eric Ruff declined to discuss any specific decisions on the Raptor programme to journalists, but said Defence Secretary Donald Rumsfeld had spoken with lawmakers in recent days "to discuss long-term
modifications to the tactical fighter programmes".
Ruff added that the Pentagon's proposals ensured that the F/A-22 and another aviation priority, the F-35 Joint Strike Fighter, "would remain healthy".
A Pentagon decision to cut back - which Congress must still approve - comes as the Bush administration is pressing all agencies to scale back spending requests for the fiscal year 2006 budget.