SCT Controller described an unsafe event that involves traffic on the KAYOH4 STAR and skydiving activity near Perris Valley. The reporter recommended moving the STAR and/or limiting the altitude of the skydivers.

Narrative

Air Carrier X was flying the KAYOH4 Arrival; which routes aircraft from BANDS to HDF VOR to KAYOH intersection. There is a skydiving zone approximately 2 miles from HDF VOR. This is a very active jump zone. If we leave the KAYOH4 arrivals on the STAR; then virtually every arrival is traffic for every jump aircraft. As such; it is common practice to route the arrivals from BANDS to KAYOH; thus avoiding the jump zone. This morning; I had a string of about 5-6 arrivals on that particular route and I was giving my normal clearance: 'After BANDS; proceed direct KAYOH;' to avoid the jump zone. Aircraft Y was the jump aircraft that was up and down in the zone. According to the Supervisor who reviewed the tape; I failed to give Air Carrier X direct KAYOH for some unknown reason; so he was headed right for the jump zone. Because direct KAYOH brings arrivals close to; but not over; the jump zone it is sometimes hard to tell if they aren't going direct. Because I thought I had given Air Carrier X direct KAYOH; I was expecting him to come close; but not go through the jump zone. I didn't notice that he was approaching the jump zone until the last moment. I attempted to turn Air Carrier X out of the way and stop the skydiving operation until the traffic was clear; but aircraft Y was already dropping skydivers. Air Carrier X said he had the jump aircraft in sight and that the jumpers were about a mile from his wing. After the event; Air Carrier X and I had a small discussion about what happened. Aircraft Y indicated he wanted to call the facility to find out what happened and why.Why we have a STAR that routes every arrival virtually right over a busy jump zone is a mystery to me. The KAYOH STAR requires Controller action (and follow-through) on virtually every arrival to maintain separation from the jump zone. This arrival needs to be moved a few miles northwest to avoid the jump zone completely. Also; allowing the jump zone to operate 14;500 FT and below in such congested airspace is a safety issue. Jump operations should be capped much lower (9;500 FT) to allow us more room to vector the arrivals or to leave them on the STAR as it was designed. This would produce less frequency congestion; less vectors and reduce the workload in the HEMET Sector.