Is it defamation to criticize conduct of public servant ?
Exception No. 2 to Sec. 499 IPC says:
“Public conduct of public servants- It is not defamation to express in good faith ANY OPINION whatever respecting the conduct of a public servant in the discharge of his public functions, or respecting his character, so far as his character appears in that conduct, and no further.”
Even if this is exception, it may have to be proved in trial and in trial, opponent will get opportunity to cross examine complainant.
Best advice is: Do not defame anyone.