The film? No, I’ve barely seen it. Writer/director John Milius is famously the most out-there right-wing member of the ‘70s New American cinema circle and is the likely basis for Walter from The Big Lebowski, so take that as you will.
The stories emerged parallel to the triumph of fascism in Germany, but I’m unaware of any evidence that Howard was influenced by this, and his view of the fate of civilizations, even or especially great civilizations, did not track with visions of the triumph of the will.
As far as anything I’ve read goes, Howard was a home-grown American racist, with his thinking strongly influenced by West Texas frontier history and culture. But I wouldn’t call him a fascist – he was way too much into the rugged individualist thing – unless you take the somewhat contentious agrarian anti-modernist view of fascism. Howard’s belief that civilization was unnatural and doomed to fall back into barbarism doesn’t jibe either.