Rosie O'Donnell got into a heated showdown over abortion with CNN's S.E. Cupp during a 'View' test show taping with Whoopi Goldberg ... who ended up taking a thinly-veiled shot at Barbara Walters. 

Production sources at "The View" tell us Cupp -- who's vying for the conservative role on the show -- had a "nasty" debate yesterday over the Australian couple making headlines for asking their surrogate to abort a Down syndrome baby.  

We're told things escalated when Whoopi jumped in and asked Cupp if she ever had to make a decision about abortion. That shut everyone up momentarily ... until Rosie chastised Cupp, saying she didn't want another Elisabeth Hasselbeck.

Here's where Babs comes in. After the taping ... Whoopi -- in front of producers and several potential replacement hosts -- said she'd been "working with a cranky 85-year-old woman who's mad about everything for 2 years, and I need a break."

Hard to tell who Whoopi was really upset with -- Rosie or Cupp -- but the shot at Barbara was undeniable.

As for Cupp ... doesn't sound like she left on Rosie's good side -- but then again ... that may be exactly what "The View" needs.