Is it possible for the government to censor bitcoin by blocking ports?
Is it possible for the ISPs to block these ports of bitcoin clients?


Yes, it is. It is fairly trivial for most ISP's to control ports.


  And, therefore censor bitcoin?


Not easily. It is possible to configure Bitcoin Core to operate over the Tor network. Tor itself can be configured to run even behind a fascist firewall (it has settings labelled such), although, I encourage all to only act in a lawful manner.

Similarly, it is possible to configure Electrum wallet to operate over Tor.