what organization deals in counterintelligence at the highest level and how is it possible to apply for a job at that particular organization
Research and Analysis Wing (RAW) deals with tha counter intelligence at international level.
To join RAW survives , candidates should give Group A Civil Services exam under the Central Scheme. They have to clear all the stages of Civil Service Examination and only the qualified candidates are allowed to write the RAW examination.
Hope this helped you.