The meeting has been dubbed a "beer summit" in the press, and was an effort to make amends after Prof Gates was arrested at his home two weeks ago.

During that incident police received a call that two men might be attempting a break-in at a house in Cambridge, Massachusetts, home to Harvard.

It turned out that Prof Gates was merely attempting to enter his own home when the door jammed.

However Gates and Crowley exchanged heated words, and the professor was arrested for disorderly conduct.

Mr Obama added to the controversy when he said police had "acted stupidly" by arresting his friend after establishing that Gates had been in his own home.

Last week Mr Obama called Crowley, a distinguished police officer, to express regret over his statement, and to invite the police officer and Gates to the White House for a reconciliatory beer.

Before the beer summit, Mr Obama said he was ``fascinated with the fascination about this evening.''

"I noticed this has been called the beer summit. It's a clever term, but this is not a summit, guys. This is three folks having a drink at the end of the day and hopefully giving people an opportunity to listen to each other. And that's really all it is,'' Mr Obama said.

An impromptu addition to the happy hour gathering was Vice President Joe Biden.

The four drank from clear glass mugs, and White House officials said Mr Obama drank Bud Light, Prof Gates was served Boston local brew Sam Adams Light, and Sgt Crowley drank Blue Moon.

The vice president drank a low-alcohol Buckler.