Not in the gmail app. The people app, calendar app and gmail app are all separate apps that work with each other. On the gmail website they are combined.
If you mean when someone sends you an invite via a .ics file, you can do what you ask in gmail on the web but not in the app. There are 3rd party apps and plugins that are supposed to work but i have not found one yet.
I got it to partially work. Go to your calendar settings on the web. (google.com/calendar). Towards the bottom you will see this:
Automatically add invitations to my calendar:
Yes, but don't send event reminders unless I have responded "Yes" or "Maybe"
No, only show invitations to which I have responded
Choose either the first one if you want to accept any invitation or the 2nd one. You can click on the event in your calendar and choose to respond or not. You can also delete it at that time.
Hope that helps.