Washington, July 25 - US President Barack Obama is seeking to douse a raging racial firestorm with an expression of regret for saying that police had 'acted stupidly' in arresting a black scholar and an offer to patch up with beer at the White House.

'Because this has been ratcheting up and I obviously helped to contribute ratcheting it up, I wanted to make clear in my choice of words I think I unfortunately gave an impression that I was maligning the Cambridge Police Department or Sergeant Crowley specifically,' Obama said Friday.

'And I could have calibrated those words differently,' he added in a surprise appearance in the White House press briefing room shortly after he spoke by phone to Crowley.

Crowley, who had last week arrested Henry Louis Gates -- a prominent scholar of African-American studies at Harvard, suggested Obama invite him and Gates to the White House for a peace-making beer and a plan was in the works to do so, Obama said.

Obama later called Gates, had a positive discussion, told him about his phone call with Crowley and invited him to join Crowley at the White House in the near future, the White House said.