May 23 (Bloomberg) -- U.S. Senator Hillary Clinton's presidential campaign is in formal talks with Senator Barack Obama's campaign about becoming his vice presidential running mate, CNN reported, without citing anyone specific.

The two Democratic campaigns are talking about ways for Clinton, from New York, to drop her bid for president that may include joining the Illinois senator's ticket, CNN reported. Talks are in a ``very preliminary'' stage and are described as ``difficult,'' the network said.

To contact the reporter on this story: Chris Dolmetsch in New York at cdolmetsch@bloomberg.net.

Last Updated: May 23, 2008 08:21 EDT