Who is Assessing Officer ?????????

Only one of the following can be assessing officer

Joint Commissioner of Income Tax

Deputy/Assistant Commissioner of Income Tax

Income Tax officer

An assessing Officer is a person who has jurisdiction to make assessment of an assessee, who is liable to tax under the Act. The designation may vary according to the volume of income/nature of trade as assigned by the Board. It may be an Income-tax Officer, Assistant Commissioner, Deputy Commissioner Joint Commissioner or an Additional Commissioner. 

I think you want to know the code for Assessing Officer for Income Tax. so please go thru following link

ASSESSING OFFICER THE FOLLOWING ARE ASSESSING OFFICERS-

JOINT COMMISSIONER - RANK 1

ASSISTANT & DEPUTY COMMISSIONER - RANK 2

INCOME TAX OFFICER - RANK 3

FOR ONE ASSESSMENT YEAR AN ASSESSEE CAN HAVE ONLY ONE ASSESSING OFFICER.