In a federal lawsuit filed today, Lukasz "Dr. Luke" Gottwald says The Bellamy Brothers launched a "smear campaign" by claiming Brit's hit -- co-penned by Gottwald -- was just a knockoff of their 1979 song ... "If I Said You Had a Beautiful Body Would You Hold It Against Me?"
Gottwald also claims the Brothers' attack was "a publicity stunt aimed to increase their record sales ... and to combat their dwindling relevance." Ouch.
In addition to damages for defamation ... Gottwald wants a court order stating once and for all Britney's song has nothing to do with the BB's song.
The Bellamy Bros. rep didn't immediately return a call for comment.