This is a tricky question.
It depends on both how you use the domain and how confusingly similar is your domain
to the governments organization name.
If for example you owned "WhiteHouse.com" and masked it so it will appear like it is the true White House's website, it would have been very wrong and unlawful behavior.
But if you would have used it for commercial purposes, like advertising promo codes while noting the true purpose of the website, this might have been better.
Since it is hard to guess the reaction of a government organization when using their names, it is advisable to not use them even for other usage.
Since some government organizations also fill trademarks on specific names, usage of a name may be a catalyst to a UDRP or other legal actions.
There are many good domains which are not composed of government organization names out there which are available, best to search for them and register them.
I'm not an expert as to trademarks and legal issues(Also: not a lawyer).
I believe it will best to read different policies of ICANN and search for cases there was an issue between a registrant and organization/s.
You can always ask for a legal advice in case you have an issue(lawyer).
