Speaking at the CBI's annual conference on Monday, the BBC chief said he wanted a debate with the public on "what would Britain look like without the BBC?".
The director-general praised the corporation as "unbelievable value for money", but he admitted that it needed to win back the public's confidence that it knew how to spend it.
"We have to get used to spending licence fee payers' money as though it is our own," he added.
The BBC boss pointed to the controversial plans mooted in 2010 to close BBC Radio 6 Music and its Asian Network as examples of the public fury that could be sparked by the corporation being forced to cut services.
Lord Hall's warning came after Tory chairman Grant Shapps recently suggested that the corporation could be forced to share part of its £3.6 billion in TV licence fee revenues with other broadcasters, or see it cut outright, if it fails to improve transparency.
The Tory chair said the £145.50 annual fee would be "too much" if it failed to reform, and added: "They are raising £3.6bn through the licence fee, which is a tax, and, quite rightly, the public wants to have sight of how the money is spent."