Login for contributors

Hi all,

I was thinking to make a guest posting section on my blog where people could register and then with signing in could write their posts.
I ‘ve seen that there is a user role “contributor” which can write posts but cannot publish them, which is perfect for me as administrator to have the final word of what the people can publish.

What I want to ask is the following.
Is there any way by coding(instructions or tutorial) or with a plugin that I could set every new registered user directly as a contributor instead of a member?

regards,

Dinos