He told MPs that areas devastated by the worst bushfires in Australia's history would be rebuilt "brick by brick" and "school by school".
Residents in parts of Victoria state are still on alert as more than a dozen fires continue to burn uncontrolled.
Crime scenes
Victoria State Police Commissioner Christine Nixon has launched Operation Phoenix, vowing to catch anyone who started a blaze.
Mr Rudd told parliament the people of Victoria were not alone in this disaster
One site where arson is suspected is Gippsland, east of Melbourne, which is among a number of sites which have been sealed off as possible crime scenes.
Australian Attorney-General Robert McClelland said suspected arsonists could face murder charges.
"We are left speechless at the thought and the possibility that some of these fires may have been deliberately lit," Mr Rudd told the Canberra parliament.
"Let us attend to this unfinished business of the nation and come to grips with this evil thing."
NICK BRYANT'S AUSTRALIA
One man said he hardly had time to react let alone move, so fast were the advancing walls of flames.
The current official death toll is 181, but Victoria State Premier John Brumby has warned that dozens of bodies remain unidentified, with others unrecovered, and the final toll is likely to exceed 200.
Ms Nixon said rescuers were carrying out a thorough search of charred areas.
"Road by road, house by house, we are working our way through," she said.
"As we go into areas now that we haven't been able to get into before, we believe we'll find many more."
HOW BUSHFIRES SPREAD
1 Fires start in hot dry windy weather 2 Embers blown ahead of fire front 3 Spot fires start where embers land
Forensic investigators from around the country, including experts who helped to identify those killed in the Bali bombings in October 2002, have flown in to help with the operation.
Mr Brumby has announced a judicial inquiry into the disaster, and authorities will review current policy on bushfires, such as allowing homeowners to stay and defend their properties.
Rebuilding
Mr Rudd pledged that damaged communities would be rebuilt, with no limit on federal spending, and he appealed for charitable donations.
The Australian Red Cross said A$31.2m (US$21m; £14m) had been donated by individuals, local authorities in Australia and corporations.
It has appealed for blood, money and clothes, as some people escaping from the fires fled their homes with only the clothes they were wearing.
US President Barack Obama was among a number of leaders from around the world who called Mr Rudd to offer condolences and help.
Talk of arson in the town of Whittlesea, north of Melbourne, provoked immediate fury, reports the BBC's Phil Mercer.
The thought that some of the devastation was man-made is, to many locals, incomprehensible, he reports.
A record heat wave and changing wind direction on Saturday helped fan the flames.
Many people are searching for loved ones among the survivors taking refuge in Victoria's relief centres.
Relatives concerned about family members in the affected areas can contact the Australian Red Cross 24-hour helpline on (0061) 393283716 or, from the UK, the British Red Cross international tracing and message service on 0845 053 2004.
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