MD80 CREW HAD TCASII RA WITH COMPANY ACFT IN SCT CLASS B AIRSPACE.

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NMAC. LEVEL AT 10000 FT; INBOUND TO SMO; TCASII GAVE A YELLOW TFC ALERT. TFC WAS CLBING AND WAS 400 FT ABOVE OUR ALT AT THE 12:30 O'CLOCK POS AND ABOUT 5 MI AND MOVING TOWARDS 1 O'CLOCK. ATC GAVE TFC ALERT COMPANY ACFT CLBED ABOVE THEIR ALT ON THE GORMAN DEP AND IS STARTING BACK DOWN. I KNEW THAT IS 9000 FT FROM PAST EXPERIENCE. TCASII ISSUED A SMALL DSCNT RATE. I STARTED THAT. I VISUALLY PICKED UP THE ACFT. THEY WERE NOW DSNDING AT A RAPID RATE. TCASII WANTED US TO DSND FASTER. THAT WOULD HAVE PUT US RIGHT INTO THE ACFT. I TURNED TO AVOID THE ACFT. WE WERE AT 9500 FT AND ABOUT 1 MI AWAY WHEN WE AVOIDED THE ACFT. I CLBED BACK TO 10000 FT AND CONTINUED THE ARR. ATC GAVE US A HDOF AND SAID THANK YOU TO US. A FEW PAX SAW THE ACFT AND MADE COMMENTS ABOUT IT AS THEY DEPLANED. THAT WAS PRETTY CLOSE AND A LITTLE EXCITING AND THANK YOU FOR THAT TURN. I BELIEVE AT THE RATE THINGS HAPPENED TCASII COULD NOT GIVE THE CORRECT INFO FOR THE RAPIDLY CHANGING SIT. SUPPLEMENTAL INFO FROM ACN 515157: LOCATION: SMO 261 DEG RADIAL; 14 DME. DURING TURN IN ON THE SAADE ARR; WE RECEIVED A CALL FROM ATC ABOUT A TFC ALERT AND AT THE SAME TIME WE RECEIVED A TCASII TFC ALERT. THE CTLR BEGAN TO ISSUE INSTRUCTIONS. THE RA WAS COMMANDING A DSCNT OF 2500 FPM AND THE PF ACQUIRED THE TARGET VISUALLY. THE CAPT ACTING AS PF MANEUVERED THE AIRPLANE LATERALLY TO THE R TO GET THE TARGET MOVING ACROSS THE WINDSCREEN. THE RA WAS COMMANDING A DSCNT WHICH IF FOLLOWED WOULD HAVE MADE THE ENCOUNTER WORSE. WE WERE AT 10000 FT AND THE TARGET ACFT WAS DSNDING THROUGH OUR ALT. THE TARGET ACFT PASSED WITHIN 1 MI OF OUR ACFT.