TMZ spoke with Howard Scott -- vocalist and a founding member of War -- who tells us he's "shocked" the rappers were inducted before his band, saying, "We were cranking out gold records when they were still in diapers."

Scott adds, "How could the Beastie Boys get in before us when they sampled War's music on their first album?! I'll eat their platinum records!"

The singer had been pretty hopeful his group would finally be inducted into the HOF this year ... and says the disappointing news "felt like I was kicked in the back of my britches."