* Bairstow comes in for Prior, Panesar replaces Swann
* Australia win fourth straight toss of series (Adds quotes, details)
By Ian Ransom
MELBOURNE, Dec 26 (Reuters) - Australia captain Michael Clarke won the toss and elected to bowl in the fourth Ashes test in Melbourne on Thursday as England captain Alastair Cook confirmed that wicketkeeper and vice captain Matt Prior had been dropped.
Yorkshire's Jonny Bairstow replaces Prior, who had been in poor form with the bat and endured a wretched match behind the stumps in the third test in Perth, where Australia sealed the five-test series 3-0 to win back the coveted urn.
"Very difficult decision," Cook said of Prior in a pitchside interview. "We felt a bit of time out of the firing line would do him good."
England have also named spinner Monty Panesar in place of Graeme Swann, who retired from England and first-class cricket during the week.
Clarke, who has not lost a toss in the series, sprung something of a surprise by sending his men into the field on an overcast day at the Melbourne Cricket Ground, where rain showers are forecast.
The MCG's drop-in wicket generally provides something for the bowling team in the first session but quickly flattens out to become more batsman-friendly as the day and the match progresses.
"I can't believe I'm saying this, but we'll bowl. The overhead conditions are good," Clarke said.
"I think there's enough moisture and grass on the wicket.
"I do think it's going to be quite slow so we're going to have to execute well this morning."
The hosts named the same side that won in Brisbane, Adelaide and Perth, with injury-prone paceman Ryan Harris deemed fit despite suffering knee soreness.
England paceman Stuart Broad retains his place despite a doubt over his fitness after he was struck on the foot when dismissed lbw by a searing yorker from Australia paceman Mitchell Johnson in Perth.
Australia - Chris Rogers, David Warner, Shane Watson, Michael Clarke (captain), Steve Smith, George Bailey, Brad Haddin, Mitchell Johnson, Peter Siddle, Ryan Harris, Nathan Lyon
England - Alastair Cook (captain), Michael Carberry, Joe Root, Kevin Pietersen, Ian Bell, Ben Stokes, Jonny Bairstow, Stuart Broad, Monty Panesar, James Anderson, Tim Bresnan (Reporting by Ian Ransom; Editing by John O'Brien)