Brandi Glanville & Joyce Giraud -- Sorry, Lady Gaga ... We're Too Busy To Be In Your Video

The "Real Housewives of Beverly Hills" did a cameo in Lady Gaga's new music video -- but two prominent cast members are missing ... and it was NOT Gaga's decision to keep them out ... the women opted out themselves.

Brandi Glanville and Joyce Giraud are conspicuously absent from the video, "G.U.Y." ... and rumors swirled they had been banned by Mother Monster herself.

But sources close to the shoot tell TMZ the rumors aren't true -- Gaga wanted the ENTIRE cast for the shoot ... but Joyce and Brandi took a pass because they had previous commitments.

Gaga's rep confirms to us she extended the invite to the entire cast.

The music video is bizarre ... with images of Michael Jackson, Jesus, Gandhi and Lady G as a feathery bird-woman. But when the Housewives show up -- pretending to play musical instruments -- it's classic over-the-top Gaga.