Ed Miliband has pledged not to raise personal taxation as he reaffirmed Labour's pre-election policy of cutting the deficit in half in four years.
The new Labour leader contrasted this approach with the coalition's "cavalier" tax rises and spending cuts.
Ed Balls, passed over for shadow chancellor on Friday, has argued for the deficit to be cut far more slowly.
Mr Miliband said Alan Johnson was the "best person" for the shadow chancellor's role.
Since becoming leader, Mr Miliband has been under pressure to spell out his approach to cutting the £155bn deficit and how it differs from that of the coalition.
He told BBC One's Politics Show that he would say more about his strategy in the lead-up to the government's 20 October comprehensive spending review.
But he said he backed former chancellor Alistair Darling's four-year deficit plan in the face of calls by Mr Balls, among others, to reduce spending more slowly and over a long period.
He made it clear he would oppose any tax rises on "ordinary families" as an alternative to spending cuts but said he wanted to see a higher levy on banks.
"I am not proposing rises in personal taxation beyond those set out by Alistair Darling. Absolutely not," he said.
He said the coalition's plans for £20bn in cuts next year, allied to January's increase in VAT, would pose a "real threat" to the economic recovery - adding that its handling of last week child benefits cuts announcement was "shambolic and frankly disgraceful".
"If they [the coalition] consign our economy to low growth and unemployment, I think people will be rightly very angry. They have been warned about the scale of cuts they are undertaking.
"I think there are being incredibly cavalier about our economy."
The coalition has accused Labour of being "in denial" about the deficit and that shirking tough decisions would increase the burden on businesses and families.
Mr Miliband, who will put the fishing touches to his ministerial team on Sunday by announcing middle-ranking jobs, also defended his surprise choice of Mr Johnson as shadow chancellor,
Praising the former home secretary's intellect, experience in government and communication skills, he stressed: "He will pick up his brief and run with it in a matter of days."
Amid reports that Ed Balls was unhappy about being given the role of shadow home secretary, Mr Miliband said all his colleagues were "very pleased" with the jobs they had been given.
Earlier, Mr Johnson told the Observer cuts were being made "too quickly and deeply" and coupled with complex reorganisations of the NHS and police services, would cause "huge harm" to the country.
Pointing to the Irish Republic's descent back towards recession, he said: "We don't have to look far to see what the effect can be of cutting too deep too soon.
"Even if a double dip [recession] doesn't happen, the way this coalition is implementing these changes will fundamentally alter our community and lead to a situation where we spend years trying to repair the damage."
On the deficit, Mr Johnson said he was a "realist" and backed the four-year strategy as it was consistent with supporting jobs and growth.
On Saturday, Lib Dem Energy Secretary Chris Huhne suggested spending plans could be scaled back if economic conditions deteriorated or improved.
However, later Chief Secretary to the Treasury Danny Alexander told the Scottish Liberal Democrat conference the planned cuts were "unavoidable".
Most Whitehall departments face cuts of up to 25% over four years.