By Erik Kirschbaum

BERLIN (Reuters) - Germany's Finance Ministry is considering selling a stake of just under 50 percent in the country's motorways to allow it to develop the network's infrastructure more efficiently, Der Spiegel magazine said on Saturday.

Ownership of the 13,000 km network, the world's second largest behind the United States and famous for having no speed limits along thousands of its kilometers, is divided evenly between the federal government and the country's 16 states.

Finance Minister Wolfgang Schaeuble is studying selling off all but a tiny fraction of the latter share, leaving Berlin with a controlling stake.

It was not clear how much such a sale would raise. But the federal government receives some 4 billion euros per year for its toll on trucks.

The ministry believes that insurers and other investors in search of investments with solid yields during a prolonged phase of low interest rates would be eager to buy stakes currently held by the 16 federal states in such a motorway privatization, Der Spiegel said.

By controlling the motorways by itself, Berlin's efficiency to build and repair motorways and other parts of the network such as bridges would be greater.

Members of parliament told Reuters that Schaeuble had presented only rough outlines of his proposal to a budget committee last week, saying that the federal government would keep a majority controlling stake if it were privatized.

The idea of privatizing Germany's motorways has been floated periodically, and any sale would almost certainly have to wait until after national elections in September 2017.

Economy Minister Sigmar Gabriel, the leader of the center-left Social Democrats (SPD) who share power with Chancellor Angela Merkel's Christian Democrat-led conservatives, is not in favor.

"There won't be any privatization of the roads nor the operators of the motorways," a spokeswoman for Gabriel said.

Merkel is expected to run for a fourth term, and both the conservatives and SPD have said they do not want to continue in a grand coalition.

It was also unclear how a company running a motorway company would organize itself.

Officials said leaders of the federal and state governments agreed at a meeting on Oct. 14 that the federal government should be responsible on its own for building and operating the motorways. But the two sides are still discussing the issue.

(Story refiles to remove extraneous '??' from paragraph 5.)

(Additional reporting by Matthias Sobolewski; editing by John Stonestreet)