The RAND Corporation's experts compared jets in a war game and the Australian Broadcasting Corporation, Radio Australia's parent company, has obtained the results.
In bad news for the Australian Air Force, the report says the F-35 has inferior acceleration, climb, turn capacity and a lower top speed than Russian and Chinese fighters.
In short, it says the Joint Strike Fighter cannot climb and cannot run.
It says the US fighter which could outdo the Russian-made Flankers is the F-22 Raptor.
But the United States bans these from foreign sales.
The fighters' defenders argue it is not designed for close combat.
The RAND Corporation says a 'Plan B' is necessary and points out that if the F-35 is seen or has to engage an enemy at close range, then it will be no match for the Flankers.
Earlier this week federal Opposition MP Dennis Jensen called on the Australian Government to scrap plans to buy the F-35, saying they could leave the country vulnerable.
"The problem is, if the perceived level of our capability is not very high some nation might think that it's worth the risk to take us on for some reason or another given the perceived benefit," he said.
A spokesman for Defence Minister Joel Fitzgibbon says he is convinced the Joint Strike Fighter is the best aircraft available, but the minister has not released the air combat capability review which studied the options.