Are Katniss and clove enemies and why?

Yes, I would say Katniss and Clove are enemies. Clove despises Katniss for her high training score (11) as Clove herself only got a ten.
Katniss and Cato are enemies as well. Cato hates Katniss for her high training score and for out-smarting the careers, as well as up-staging and getting away from them, also for killing Glimmer, Marvel and the un-named D4 female.

Both Clove and Cato become obsessed with killing Katniss.