I'm looking for a 70's disco music song (basically the singer and the
name of the song)that contains this phrase:
"you could be dancing, moving with the band, holding the world in your
hands and if you're going to do whatever..." I heard the song in the
documentary "The American Nightmare" on the George Romero's section
when he talks about the 70's years...

I'm just a regular schmo trying to help.

Here are the music credits for the documentary:

Music: Karlheinz Stockhausen; Godspeed You Black Emperor!
Additional Music: Leechwoman; Yellow 6; Manuel De Fala; Frederico Mompou

Could it be that the song is not 70's disco?

Probably the most likely candidate from the above is the Leechwoman
song called "Breaker" - which is in the documentary apparently, but I
have no idea what it sounds like, or what the lyrics (if any) are.

Leechwoman is definitely not 70's disco, they're mostly hardcore
(HAAAARDcore) techno-dance : )

If there is a 70's song I don't think it's listed in these credits.

That's the problem... the song is not on the credit list.
I think is disco , because George Romero talks about the 70's and you
see people dancing on rollerblades... (could be a song from the 80's
but I don't think so...)
Thanks jimbo333!