sivaharimani, you appear to have done a good research in the subject. but you will realise when you get into the services, from practical experience, that part of the information collected by you is wrong factually. it could be because of your misinterpretation as well.
let me get a few things in proper perspective for your benefit. firstly there is this concept of taxation in the country which you must understand. the constitution of india differentiates various taxes and allots the job of collection and appropriation of taxes between the centre and the states.
income tax is levied and collected by the central govt. the officers of the income tax dept are not district officers. their jurisdiction can in many cases include multiple districts as well. coordination or supervision of levy and collection of income tax is not the responsibility of the district collectors. And income tax is not certified by the collector as you seem to think. The collector is duty bound to assist in recovery of tax arrears to govt and so is the police.
the other confusion you appear to be in is that all forms of tax are collected by
IRS officers. it is not correct.
IRS officers are responsible for collection of only income, tax, corporation tax, central excise, customs, service tax etc. other taxes like property tax, state sales tax etc are collected by the state govt. and yes, agricultural income tax is in the state list.
further if you are under the impression that all the 18 departments you listed out are headed by specialists, you are mistaken. quite a few of them are headed by the 'generalists' of the state administrative service.
district collector, however, is for most practical purposes the face of government in a district. developmental activities are routed through him and most public grievances can be settled by him. it is also pertinent to mention that in many states, this position is now very much diluted as most of the above mentioned activities are now done through the district panchayat which though not theoretically but in many ways practically independent of the collector. most developmental works are done through the zilla panchayat. After the 73rd constitutional amendment, panchayat raj institutions are gaining pre-eminence at the cost of the district collector. it is besides the point that the CEO of the ZP could possibly again be an
IAS officer.
Being the representative of the state government in the district, the DC is the first person approached by most central govt depts for liaison with state govt. the reverse is also true. For any liaison the state govt wants to have at district level with central govt bodies, the DC plays a central role. But to say that DC coordianates and supervises all central govt activities in the district is slightly far fetched. Yes it is correct to the extent that he involves himself in those areas which have substantial state govt interest.
but definitely, sivaharimani, you have done a very honest research and gathered quite some useful information on the office of the district collector. good job.