A corporate jet Captain reported an NMAC with a light aircraft in SoCal airspace.

Narrative

While in level flight at 5;000 FT over OCN VOR; SoCal approach told us we had an aircraft at 4;500 FT at our 12 o'clock. ATC also told us to maintain 5;000 FT. I replied that we were looking for the traffic and that we had the aircraft on TCAS. As we approached the traffic we were unable to gain a visual on the aircraft and I noticed the aircraft was deviating from 4;500 to 4;800 FT. I told my First Officer who was flying to be ready for a deviation or climb; shortly after I said that we got an RA with a climb command. My First Officer turned off the autopilot and began a climb to comply with the RA climb. My First Officer climbed to 6;000 FT. to avoid the climbing traffic. As soon as my First Officer started the climb I notified ATC that we were climbing and the TCAS was saying 'climb; climb' in the background on top of my transmission SoCal approach then asked us to return to 5;000 FT and I replied that we were. Right before I said we were returning to 5;000 FT the TCAS said 'Clear of conflict'. My First Officer then returned the aircraft to 5;000 FT. No other aircraft were impacted during the deviation and the controller began scolding the other traffic that caused the deviation. The SoCal controller told the other aircraft ' When I tell you to maintain an altitude because a jet is coming at you; you need to do it.' The other aircraft responded 'Yes sir; we will.' After we returned to 5;000 FT that was the end of the event and we landed without further incident.