Suppressing information always causes problem. Why didn't you mention that you have been working in Govt.? As you have suppressed your employment information, you would not be able to include your present service in case of your selection in CGL 2017.
If you resign from your present employment, there is no question of NOC. NOC means 'No Objection Certificate' from your present employer when you apply for another job. You have not done it. In case of selection, you have to resign and your resignation will be accepted if there is no vigilance case against you or is being contemplated against you and if you have not signed any bond. If you have signed any bond, then there is a provision of transfer of bond from one Govt. office to other Govt. office.
Without going into so much technical details, your present action would be: (i) preparing seriously for CGL, (ii) intimating your office about your applying for a new Govt. job, which would help acceptance of your resignation quickly in case you are selected for any Govt. job under CGL.
In future, while applying for new Govt. job, please don't suppress information and apply through proper channel (along with advance copy).
Caution: Explosive. Handle with care.