Several campaign staffers were in a room at the back of the office Thursday night when they heard the sound of smashing glass at the front and side of the building, said police Cmdr. Andrew Smith.
They found three front-door windows and a side glass door had been smashed.
No rocks or projectiles were found, and police believe one or more attackers used a tire iron or something similar to break the glass, Smith said.
"Someone could have run by and hit it with an object," he said.
Detectives believed the attack was politically motivated because no other businesses in the usually low-crime area were targeted, Smith said. No threats were made before or after the attack.
Police notified the Secret Service and FBI officials said they are assisting Los Angeles police with the investigation to determine if the incident was motivated by hate or an act of domestic terrorism.
Katie Hogan, a spokeswoman for Obama's re-election campaign, declined comment.
The office housed in a three-story building is in the Playa Vista area on the suburban west side. Plywood boards covered the broken windows and door. It wasn't known whether staffers were going to return to work on Friday.
Obama is scheduled to visit Los Angeles on Monday to raise money for his campaign.