The long term unemployed would be forced to work for their benefits under plans outlined by the Conservatives.
People claiming Jobseekers' Allowance for more than two years would have to do 12 months community work.
Tory leader David Cameron said he wanted to help people into work and end the "something for nothing culture".
PM Gordon Brown said the government was already getting tough with the long-term jobless and the Tory plans were out of date and would not work.
Under the Conservative proposals, the two-year limit on job seekers' allowance would apply to "continuous and cumulative periods of unemployment".
The party says it wants to stop people claiming for years at a time, by signing off for short periods or taking a job for a short period, then going back on benefits.
The long-term unemployed would have to take part in a 12-month programme involving "valuable improvement and amenity work in the areas where they live".
The jobless would also have to spend most of the working week at "back to work centres", run by independent groups, where they would receive training and guidance to help find a job.
All job seekers would be screened as soon as they start claiming - those with a "track record" of claiming benefits would be referred to the centres straight away. Others would be given a "grace period" to find a job.
The proposals are mainly aimed at the 68,000 on Jobseekers' Allowance for more than two years and the 16,000 on the benefit for more than five years.
The Tories have also unveiled plans to cut the number of people on incapacity benefit by 200,000.
All 2.64 million incapacity benefit claimants would be reassessed by doctors and, if passed fit for work, placed on Jobseekers' Allowance, a benefit cut of £20 a week.
In addition, jobless people who refuses a "reasonable" offer of employment would lose one month's benefit for the first job offer, three months for the second, and up to three years for the third in a "three strikes and you're out" policy.
Mr Cameron told BBC Breakfast: "We cannot go on as we are with 2.6 million people on incapacity benefit, 500,000 of them are under 35.
"Are we really saying there are half a million people in this country under 35 who are simply too ill to work? I don't think that's right.
"I think we have got to make changes and this is a genuinely thought-through and worked-out package which I think will help get more people into work and help them make better lives for themselves and their families."
Asked if working for benefits, rather than the national minimum wage, would be an affront to people's dignity, he said: "Where is the dignity in sitting at home, dependent on the state, not having a job?"
He said the idea was to "get people back in touch with work".
Asked if those forced to work for benefits would have to wear uniforms, as claimed in newspaper reports, Mr Cameron said it would be down to the companies running the schemes.
The government says the Tory sums do not add up and Mr Cameron would need to find an extra £3bn to fund his plans.
Gordon Brown said Labour's welfare-to-work policies were "far more modern, up to date and radical" than the Tory proposals, which he said did nothing to address the skills gap.
"We are being tough in saying it is a duty on the unemployed in future not only to be available for work - and not to shirk work - but also to get the skills for work. That is a new duty we are introducing," he told a Downing Street media conference.
He said the government was investing more in training and had secured agreements with firms to take on 300,000 long-term unemployed people.
Lib Dem work and pensions spokesman Danny Alexander said the Tory proposals were "hollow rhetoric designed to sound tough rather than helping people back to work".
"The real issue is how to reduce poverty and raise aspirations by ensuring everyone has access to a fulfilling and sustainable job, not cosmetically lowering the benefit claimant numbers", he added.
He said the welfare-to-work system should be simplified and "tailored" to individual needs.
Kate Green, of the Child Poverty Action Group, said British rules on claiming incapacity benefit were already among the strictest in the world, and levels of fraud were small compared with the amount that went unclaimed.
"We are talking about families in real hardship struggling to bring up their kids," she said.