ACR WDB DESCENDED TO WRONG ALT AND INTO LESS THAN STANDARD SEPARATION WITH ACR MLG.

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OAK SECTOR 34 WAS S-TURNING AS THEY CAME OUT OF HOLDING AT MODESTO. I WAS DSNDING ALL ACFT TO FL310 AND REDUCING SPD TO 250 KTS IAS. I ISSUED A DES CLRNC TO WDB X FROM FL350 TO FL240; BUT I PUT FL310 IN THE DATA BLOCK AND THOUGHT THAT I ISSUED FL310. I WAS WATCHING SECTOR 34 WHICH WAS ADJACENT TO MINE; AND I GUESS I LOST CONCENTRATION BECAUSE FL240 COME OUT WHEN I WAS THINKING FL310. I AFFECTED A HDOF TO SECTOR 34; REDUCED HIS SPD TO 250 KTS IAS AND TRANSFERRED TO 34'S FREQ. THERE WAS SOME CONFUSION AT 34 BECAUSE THEY DID NOT VERIFY THE ALT THE ACFT WAS DSNDING TO AND THE ACFT DESCENDED THROUGH FL310 RESULTING IN A LOSS OF SEP WITH MLG Y LEVEL AT FL290. THE SECTOR 34 CTLR IMMEDIATELY CLBED WDB X UP TO FL310. I DO NOT KNOW WHY I SAID FL240 AS I THOUGHT I SAID FL310. I DO NOT KNOW HOW TO CORRECT IT. SUPPLEMENTAL INFORMATION FROM ACN 81468: AFTER OAL WE WERE CLRD TO DES TO FL240; AND WERE SHORTLY THEREAFTER HANDED OFF TO OAK CENTER AND I CHANGED FREQ TO OAK. IMMEDIATELY AFTER CHANGING FREQ; AND BEFORE I COULD RPT ON; THE NEW CTLR CALLED US AND TOLD US TO SLOW TO 250 KTS AND TURN LEFT TO 210 DEGS. WE CONTINUED OUR DES TO FL240; WHICH WAS SET IN OUR ALT ALERT WINDOW AND INSERTED IN THE FMC. AS WE WERE PASSING THROUGH 30600' OR SO; THE CTLR SAID; 'WDB X; IMMEDIATELY PULL UP; CLB TO (?); TFC 12 O'CLOCK FL 290!' WE THEN SAW THE TFC AT 11 O'CLOCK HDG SBND ABOUT 3-5 MI DISTANT AND BELOW US; SO WE LEVELED OFF AT ABOUT FL310 OR JUST BELOW. THERE WAS STILL SOME CONFUSION AS TO JUST WHAT THE CTLR WANTED ON THE ALT. WE MAINTAINED FL310 TILL I WAS ABLE TO BREAK INTO THE FREQ TO GAIN FURTHER INSTRUCTIONS. THE CTLR CAME BACK; 'YOU WERE CLRD TO FL310;' AND I REPLIED; 'NEGATIVE; WE WERE CLRD TO FL240 AND WE ARE NOW AT FL310; WHAT ALT DO YOU WANT US AT?' WE THEN GOT CLRNC LOWER. SEVERAL MINS LATER; THE CTLR ASKED IF WE HAD RECEIVED THE CLRNC TO FL240 ON THIS FREQ OR THE PREVIOUS FREQ. I REPLIED IT WAS THE PREVIOUS FREQ. WE THEN CHANGED FREQS AND PROCEEDED TO SFO. I BELIEVE THAT FACTORS CONTRIBUTING TO INCIDENTS ARE THAT CTLRS ARE GIVEN TOO MANY ACFT TO HANDLE AT ONE TIME; AND ON MORE THAN ONE FREQ. I HAVE BEEN FLYING FOR AN AIRLINE FOR ALMOST 20 YRS; AND I DO NOT REMEMBER THE TFC CONFLICTS IN THE FIRST 18 BEING AS FREQUENT OR AS LIFE THREATENING AS I HAVE OBSERVED IN THE LAST 2 YRS. WE NEED MORE QUALIFIED AIR TFC CTLRS--IT SEEMS DANGEROUS TO NOT REHIRE THE QUALIFIED CTLRS WHO WERE FIRED IN 1981 FOR POLITICAL REASONS. SAFETY IS NOW BEING COMPROMISED.