TWR CLEARED WDB TO CROSS RWY 28L WHEN SECOND WDB WAS ON SHORT FINAL AND HAD BEEN SIDESTEPPED TO THAT RWY. CLOSE PROX. OPERATIONAL ERROR.

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APPROX XXXX TOLD BY TWR TO PULL TO RIGHT SIDE OF TXWY AT 28L HOLDING POINT AND EXPECT DELAY FOR 28R. PULLED TO RIGHT SIDE AND SMALL TURBO PROP ACFT PULLED TO MY LEFT; SLIGHTLY BEHIND AND STOPPED. WE WERE THEN CLRD TO CROSS 28L AND HOLD SHORT OF 28R. APPLIED PWR ON WING ENGS ONLY (DUE TO CLOSE PROX OF SMALL TURBO PROP); TURNED LEFT IN FRONT OF TURBO PROP AND STARTED TO CROSS RWY 28L. WE THEN HEARD TWR ASK AN ACFT IF THEY COULD SIDESTEP TO THE LEFT RWY. I LOOKED OUT RIGHT SIDE WINDOW AND SAW WDB Y IN A RIGHT BANK; RIGHT OF CENTERLINE; OVER THE APCH LIGHTS FOR 28L. OUR ACFT WAS NOW 10' OR SO ONTO THE RWY AND STOPPING WAS NOT POSSIBLE. APPLIED FULL PWR TO ALL ENGS; CLRD 28L AND VIGOROUSLY BRAKED TO KEEP FROM SLIDING ONTO RWY 28R. I TOLD TWR; 'THAT WAS STUPID!' THE WDB Y PLT SAID; 'I AGREE.' THE TWR THEN CLRD US FOR 'IMMEDIATE TKOF.' WX WAS RPTED BY ATIS INFO-S WAS 1 1/2 VIS; RAIN AND FOG -X 2000' OVCST. NOT JUST POOR JUDGEMENT; BUT LACK OF JUDGEMENT; PROBABLY LACK OF EXPERIENCE AND PUSHING THE ATC SYS BEYOND ITS LIMITS.