When the N.F.L. agreed in 2012 to donate tens of millions of dollars to concussion research overseen by the National Institutes of Health, it was widely seen as a positive turning point in football’s long history of playing down the long-term effects of brain injuries on players. At the time, the league said that it would have no influence over how the money was used.

But the league and its head, neck and spine committee worked to improperly influence the government research, trying to steer the study toward a doctor with ties to the league, according to a study conducted by a congressional committee and released on Monday.

“Our investigation has shown that while the N.F.L. had been publicly proclaiming its role as funder and accelerator of important research, it was privately attempting to influence that research,” the study concluded. “The N.F.L. attempted to use its ‘unrestricted gift’ as leverage to steer funding away from one of its critics.”

The N.F.L., in a statement, said it rejected the accusations laid out in the study, which was conducted by Democratic members of the House Committee on Energy and Commerce. “There is no dispute that there were concerns raised about both the nature of the study in question and possible conflicts of interest,” the league said. “These concerns were raised for review and consideration through the appropriate channels.”