An air carrier pilot reports a close encounter with a hang glider near PETIS Intersection on the ZIGGY FOUR STAR at 9;000 FT descending to ONT.

Narrative

While on the ZIGGY 4 arrival to ONT; we were told by SoCal approach that there had been reports of hang gliders and a powered parasail (by a previous Air Carrier) 'in the pass' (somewhere between HITOP and PETIS). We had initially been cleared to 8;000 FT; and 'direct PETIS' -- normally we would have expedited down to that altitude. However; given the information; we decided to stop our descent at 9;000 FT and continue on our present southeasterly heading to avoid the hang gliding activity. After passing approximately 10;000 FT I observed several hang gliders 2;000-2;500 FT below us. Moments later I saw one through my aft window; that was probably 500-800 FT below and approx 1/4 mile laterally from our present position. While this incident didn't result in a collision -- we had been cleared to 8;000 FT and had been cleared; 'Direct PETIS'. Had we continued down; and turned; the hang glider likely would have been much; much closer. The Controller was doing his best to provide separation from the hang gliders as could be expected from a group of aircraft with which he was neither talking to; nor had on radar. After this event was over; we continued on to ONT and landed normally. The event occurred due to hang gliding/parasailing activity on a published STAR. I would suggest creating procedures to keep commercial aircraft away from this area when hang gliding activity is occurring. I would also suggest informing said hang gliders of the extreme danger that they are subjecting themselves to by operating without conferring with SoCal Approach. I would expect that proper communication could ensure safety for all involved.