In a speech to Reform, a think tank, Cameron is expected to pledge a cut in the number of quangos (quasi-autonomous non-governmental organisations) in a bid to save costs and create greater accountability.
Under the plans Ofcom will lose its ability to make decisions about policy. Instead it will focus on its "technical function" of enforcing existing rules.
Speaking to the BBC Breakfast programme Cameron said there was a need for quangos to serve technical functions such as inspecting power plants or the Office of National Statistics which provided information -- but, he said, in many cases their growth has spiralled out of control.
Cameron said: "In too many cases these organisations have got bigger and bigger.
"They spend about £64bn a year, they start having their own communications departments, their own press officers -- they start making policy rather than just delivering policy -- and their bosses are paid vast amounts of money."
There are 790 quangos costing around £35bn a year. The Conservative announcement comes as the government announced a public spending review.