Our local radio station, radio free brattleboro, is currently documenting
community support to show the FCC that indeed, we have the "authority to
operate" as granted to us by the public, who own the airwaves....Our lawyers
have advised us that since the FCC has not defined what "authority to operate"
is, we can define it as community support.

Of course. We all know the FCC has never heard THIS argument before.

If this is an example of the legal advice you're getting, fire them and get
different lawyers....ones with communications law experience, who can tell you
where you really stand legally.