R&B singer Chris Brown has pleaded guilty to assaulting former girlfriend Rihanna and will be sentenced to 180 days of community service for the attack, lawyers said.

Lawyers for Brown, who had earlier pleaded not guilty to assault charges, announced the deal as the singer appeared in Los Angeles Superior Court for a preliminary hearing into the case.

The plea deal sees Brown, 20, escape a jail sentence for his February 8 attack on singer Rihanna, which occurred as the couple drove home from a pre-Grammy Awards party.

The incident shocked the music world and left Rihanna nursing cuts and bruises to her face, forcing her to cancel a scheduled performance at the Grammys in Los Angeles later that day.

Brown issued an apology following the incident, saying he was "sorry and saddened" by the events and that he was seeking the counselling of his pastor, family and friends.

Affidavits filed in the case alleged Brown slammed Rihanna's head against the window of a car the couple were travelling in before repeatedly punching and biting her.

Under the plea deal, Brown will be placed on probation for five years and must perform 180 days of "labour-oriented" community work in his home state of Virginia, prosecutors said.

He will be formally sentenced at a hearing in August.

Rihanna appeared in court with her lawyer after Brown had left the packed courtroom.