CAPT DSNDS ON APCH WITHOUT CLRNC.

Narrative

I WAS THE FO ON THIS FLT AND WAS TALKING WITH ATC. THE CAPT WAS FLYING THE ACFT. WE WERE PROCEEDING DIRECT TO CIVET INT; CLRED TO DSND TO FL220. WE LEVELED AT FL220 AND I ASKED THE CTLR IF WE WERE GOING TO GET THE REEDR 3 ARR. THE ATIS SAID LAX WAS LNDG ON 7R AND 6L. THIS IS DIFFERENT AS LAX LANDS TFC MOST OF THE TIME ON 25L AND 24R. THE CTLR CLRED US FOR THE REEDR 3 ARR AND TO MAINTAIN FL220. I WAS LOADING THE FMS FOR THE REEDR 3 ARR; ATC GAVE US SEVERAL SPD CHANGES AND TA'S. SEVERAL MINS LATER; ATC ASKED WHAT OUR ASSIGNED ALT WAS. I SAW THAT WE WERE DSNDING AND THAT FL190 WAS IN OUR ALT SET WINDOW ON THE FMS PANEL. THE CAPT SAID THAT HE THOUGHT WE HAD BEEN CLRED TO FL190. I DON'T RECALL THAT. THE CTLR SAID WE WERE CLR OF TFC AND TO DSND TO 14000 FT. I THINK THE CONTRIBUTING FACTOR TO THIS WAS NOT KNOWING WHAT ARR TO EXPECT UNTIL WE WERE ALMOST AT CIVET INTXN. MOST OTHER ARPTS GIVE WHAT ARRS TO EXPECT ON THE ATIS. THAT WAY THE ARR CAN BE LOADED INTO THE FMS WELL IN ADVANCE. WE WERE VERY BUSY IN THE COCKPIT WHEN THIS HAPPENED; CHANGING SPD; ALT HDGS; LOOKING FOR TFC AND LOADING DATA INTO THE FMS FOR AN ARR WHICH IS RARELY USED.