"I'm absolutely ready to make tough decisions. There will obviously be changes in Perth."
England are seeking their fourth successive Ashes series victory, a feat not achieved since 1890, but have been largely outplayed so far.
They reduced Australia to 132-6 on the opening day in Brisbane but let that position slip and were bowled out for 136 and 179 to lose by 381 runs.
Then in the second Test at Adelaide, having seen the Australians amass 570-9, the batting failed again, as the tourists were all out for 172.
There was improvement in the second innings, with Joe Root, Kevin Pietersen and Matt Prior making half-centuries in a total of 312 but it was not enough to avert a 218-run defeat.
"We haven't been skilful enough for long enough to get into better positions in the matches," Flower said.
Flower critical of England batsmen
"That's the crux there. Our batting failed three times in a row."
But he said it was too "simplistic" to suggest England were guilty of a "lack of fight", adding: "We've been outplayed in these two Tests, very obviously.
"We have a history of playing competitive cricket.
"I know we have a mixture of experienced and young players, but a lot of these players have done some amazing things for England in the recent past, and we are going to have to fight for that to happen again."
England's top order was disrupted when Jonathan Trott, who averaged 89 when they won 3-1 in
Australia in 2010-11,
left the tour with a stress-related condition after the first Test.
They now travel to the Waca where they have lost their last six Tests and won only one of the 12 Ashes matches played there since 1970.
Eng 2010-11 Ashes averages
A Cook: 127.66 (highest 235 not out)
J Trott: 89.00 (highest 168 not out)
I Bell: 65.80 (highest 115)
K Pietersen: 60.00 (highest 227)
M Prior: 50.40 (highest 118)
Yorkshire trio Tim Bresnan, Jonny Bairstow and Gary Ballance are candidates to strengthen the batting, while tall pacemen Steven Finn and the uncapped Boyd Rankin, along with Bresnan, are bowling options.
England gave a debut to Durham all-rounder Ben Stokes in Adelaide and Flower was impressed with the 22-year-old, who took 2-70 in the first innings and made 28 with the bat in the second innings.
Current series averages
J Root: 43.33 (highest 87)
I Bell: 38.33 (highest 72 not out)
M Carberry: 28.50 (highest 60)
K Pietersen: 25.25 (highest 53)
A Cook: 20.50 (highest 65)
M Prior 18.25 (highest 69)
"Stokes showed tremendous all-round potential and handled himself well," said the coach, who added that Root, who made 87 at number three in Adelaide - England's highest score of the series thus far - "has shown real glimpses of the player he can be".
Australia's left-arm paceman Mitchell Johnson has been the scourge of the England batsmen, taking 17 wickets in the first two Tests and consistently bowling well in excess of 90 miles an hour.
Flower denied that his players were intimidated and said: "I think he's bowled at a good pace but that's what you expect in Test cricket. It's one of the really exciting aspects of playing Test cricket and it's really exciting for the spectators to watch.
"One thing I would say about playing fast bowling is that our batsmen have to display the combination of skill and determination to bat long periods against it, because if we do expose our lower order they will struggle against that sort of pace. So the responsibility lies with the batsmen."
Alec StewartEx-England captain & Test Match Special summariser
"[Leaving out Swann] is not a decision England should take lightly because he is a world-class spinner and has played a very important role in the successful England set-up for a number of years. Throw in his excellent catching at slip and the potential lower order runs he offers and it becomes clear why it would be a huge call."
Meanwhile wicketkeeper Prior,
writing in the Daily Telegraph,
said the Adelaide collapse was "as embarrassing a performance as I have been involved in with England."
He added: "You are representing your country and that is not a performance anybody expects from this team. We were horrendous and there have been honest chats and words spoken."
Spinner Graeme Swann, England's leading wicket-taker with 26 in the
3-0 home series
win earlier this year, has taken only four wickets in the opening two Tests at a cost of 99.25 runs apiece, and his place has come under scrutiny.
Former England captain Alec Stewart
told the BBC:
"Australia's tactic of taking on the England off-spinner has been very successful and at Perth, where spinners have traditionally struggled to make a major impact, England may be better served by going with a fourth seamer and relying on Root and Pietersen to provide the part-time slow-bowling options."
Swann said in the Sun: "Momentum is a huge thing in sport, the most difficult thing is to get it back but there's plenty of fight left in this team."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.