Fixed term/permanent posts

hello, I was hoping for a bit of advice if you would be happy to help.

I work for a local authority on a permanent contract. I just passed my three year mark. I have applied for a job within the same local authority but another team. They are hiring both permanent and fixed term posts. if they offer me a fixed term contract how would this affect me? if they offer me a year that takes me over 4 years continuous service, would this mean they have to keep me as permanent?