Labour wants to work with the Government to turn around the universal credit reforms and "hopes" to run at the next general election pledging to keep the new system.
In a speech in North London, shadow work and pensions secretary Liam Byrne levelled personal attacks at Iain Duncan Smith, claiming there "seems to be something very wrong in the mind" of the the Work and Pensions Secretary because of his failure to deliver reforms.
He said he would be writing to Mr Duncan Smith urging him to convene cross party talks with civil servants to save the flagship universal credit reforms from becoming a "sinking ship".
Universal credit is intended to roll six current benefits - including jobseeker's allowance, working tax credits and housing benefit - into a single monthly payment. It is currently being piloted.
Asked if he did want to save the policy, Mr Byrne said: "I hope so, I sincerely hope so, but right now we have had so much dissembling we don't know what is going on. Last year Mr Duncan Smith said there would be a million people on universal credit. I think it was also said new applications for benefits by this October would be for universal credit.
"Both of those targets have disappeared but no new targets have come back into their place. Who on earth knows what's going on? If we're going to get things straight, the first step is to put the cards on the table, tell us what is going wrong and perhaps we can work together."
In his speech to mentoring charity Chance UK, the former Treasury minister said the failure to deliver at the Department for Work and Pensions would cost the taxpayer £1.4 billion during the course of the current five year Parliament.
Mr Byrne said the biggest cost would come from extra job seeker allowance claims because of low take-up of the youth contract - insisting that, on current trends, targets would be missed by 92%, costing £457 million.
However Mr Duncan Smith's spokeswoman said Mr Byrne's figures were "nonsense".
She said: "This is a last-ditch attempt by Liam Byrne to keep his job in the shadow cabinet. Nothing more. His talk of wasted money is frankly laughable when you consider Labour have voted against £83 billion-worth of savings to the welfare budget. Labour is panicking - after a summer of discontent, here is yet another disastrous speech, void of any ideas."