Gen Hayden is currently deputy director of national intelligence

Air Force General Michael Hayden is expected to be named on Monday as Mr Bush's candidate to replace Porter Goss, who resigned on Friday.

But Democrat and Republican legislators have expressed concern at having a military man head a civilian agency.

"I do believe he's the wrong person, in the wrong place, at the wrong time," senior Republican Peter Hoekstra said.

Mr Hoekstra, chairman of the House Intelligence Committee, said there were already "ongoing tensions" between the CIA and the Pentagon.

His views were echoed by Democrat Senator Joe Biden who said the appointment could leave agents with the impression the CIA has been "just gobbled up by the defence department".

'Lost confidence'

Porter Goss's resignation after less than two years as director, in which he was given the job of reforming the agency after a series of intelligence failures, came as a surprise.

He declined to comment on his departure, telling CNN that "it's one of those mysteries".

The White House denied as "categorically untrue" US media reports that the president had lost confidence Mr Goss.

"There was a collective agreement that now would be a time that we could have a new CIA director come in and take the ball and move the agency forward," spokeswoman Dana Perino said.

A BBC Washington correspondent says the most likely reason for his departure is that Mr Goss objected to his boss, John Negroponte.

Mr Negroponte was appointed to the post of national intelligence director last year.

General Hayden is currently Mr Negroponte's deputy.