U.S. President Barack Obama pauses Friday as he speaks about the incident between Henry Louis Gates Jr. and Cambridge, Mass., police officer Sgt. James Crowley. (Ron Edmonds/Associated Press)

U.S. President Barack Obama told reporters in Washington on Friday he should have chosen his words more carefully when he said police "acted stupidly" in arresting a black Harvard scholar who is also his friend.

The remark touched off a debate over race. Obama made the conciliatory comments at an impromptu news conference after a five-minute phone conversation with Sgt. James Crowley, the Cambridge, Mass., police officer who arrested Harvard professor Henry Louis Gates on July 16.

Obama also talked about inviting both Crowley and Gates to the White House for a beer.

"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 Sgt. Crowley specifically," Obama said. "And I could have calibrated those words differently."

Obama called Crowley an "outstanding police officer and a good man." Both sides —Crowley and Gates — "overreacted" in the matter, he added.

Later, Obama said he had also spoken to Gates, but he declined to give any details about that conversation.

Earlier Friday, the police union in Cambridge rallied behind Crowley, asking that Obama and Gov. Deval Patrick apologize for their comments on the case.

Patrick said Gates's arrest was "every black man's nightmare."

Dennis O'Connor, president of the Cambridge Police Superior Officers Association, said Friday that Obama's remarks were "misdirected" and the Cambridge police "deeply resent the implication" that race was a factor in the arrest.

"President Obama said the actions of the CPD were stupid and linked the event to the history of racial profiling in America," O'Connor said. "The facts of the case suggested that the president used the right adjective but directed it to the wrong party."

In this photo taken by a neighbour on Thursday, July 16, Harvard professor Henry Louis Gates Jr. is arrested at his home in the suburbs of Boston. (Associated Press)

Officers responded to Gates's home after a woman called 911 and said she saw two black men with backpacks trying to force open the front door. The woman, Lucia Whalen, has not responded to repeated attempts for comment.

Gates, who is the director of the W.E.B. Du Bois Institute for African and African-American Research at Harvard, has said he was returning from an overseas trip when he found his door jammed. He and his driver attempted to force it open.

Gates went through the back door and was inside the house on the phone with the property's management company when police arrived.

Police said he flew into a verbal rage after Crowley, who is white, asked him to show identification to prove he should be in the home. Police said Gates accused Crowley of racial bias, refused to calm down and was arrested.

The charge was dropped Tuesday, but Gates has demanded an apology, calling his arrest a case of racial profiling.

Gates, 58, maintains he turned over identification when asked to do so by the police. He said Crowley arrested him after he followed the officer to the porch, repeatedly demanding the sergeant's name and badge number because he was unhappy over his treatment.

Crowley has refused to apologize, saying he followed protocol.

With files from The Associated Press