With voters to decide the country's future in September's referendum, Johann Lamont said Nationalists were trying to "drag" people to a "place of no return outside the United Kingdom".
The Scottish Government's pledge to massively increase free childcare after a Yes vote was branded a "patronising and cynical con" to woo female voters.
With Scots voting on independence in less than six months time, Ms Lamont focused her speech to the Scottish Labour conference in Perth on the choice facing voters then.
Instead of Scotland leaving the UK, she said Scotland should lead the UK.
As an alternative to independence, Ms Lamont said Labour would enhance devolution to create a "new power house Scottish Parliament".
She blasted the SNP's tactics, saying: "The Nationalists are running the most dishonest, deceptive and disgraceful political campaign this country has ever seen."
She added: "Their strategy is not to convince the people of Scotland - it is to drag them over the line to a place of no return outside the United Kingdom.
"Decent Nationalists throughout this country must be hanging their heads in shame at the campaign that is being run."
The SNP has set out what it describes as "transformational" plans to provide families with 1,140 hours a year of free childcare in an independent Scotland.
But Ms Lamont said: "What would be really transformational would be if this Government ever told the truth."
With the referendum approaching, however, she said the First Minister's party would "go down as conducting the worst campaign of mis-selling in history".
As well as attacking her Nationalist rivals, Ms Lamont used her speech to position Labour as the party of social justice in Scotland.
As part of new powers Labour has pledged to devolve to Holyrood, she said Labour would increase tax for those earning £150,000 or more to 50p.
This would be part of "new Scottish progressive rates of income tax," Ms Lamont said, adding it would "mean that the Scottish Parliament will be able to make our tax system truly progressive"
She also pledged that the cash raised from this would be reinvested in public services.
"The Nationalists refuse to reverse George Osborne's tax cuts for millionaires, but we will," she told party activists.
"That is powers for a purpose."
Her speech came just days after Labour's devolution commission set out the party's plans for transfer of further powers north in the event of a No vote in September.
As well as greater powers over income tax, Holyrood would get control over housing benefit, with the attendance allowance also devolved. A new Scottish Health and Safety executive would be set up, and responsibility for employment tribunals would be devolved.
Labour would also act to ensure the Scottish Parliament is "permanently entrenched and indissoluble".
"What we propose is a new power house Scottish Parliament," Ms Lamont said.
She insisted the union between Scotland and the rest of the UK was a "union of equals and partnership" and was "not a contractual union or marriage of convenience".
She said: "To lead in the 21st century, to preserve our values and advance the people's interests, Scotland needs the United Kingdom and the United Kingdom needs Scotland."
But while the SNP want Scotland to leave the UK and become independent, the Labour leader said: "I am more ambitious than that, I want Scotland to have the self-confidence to lead the UK."
Ms Lamont held out a "vision of a new Scotland - a nation renewed, prosperous, thriving and together".
She said that would be "accomplished by Scottish Labour, a re-energised, ambitious and confident party that will earn the support of the Scottish people and remove the most dishonest and detached government since the creation of devolution".
She vowed to "reclaim social justice for Scotland" as she hit out at the Scottish Government plans to "give tax breaks for the rich".
In the SNP's seven years in power at Holyrood she said they had failed to introduce a single policy "which redistributes wealth from rich to poor".
The Labour leader insisted: "We will not wear nationalist clothes, but we will rip from the Nationalists the threadbare garments they dress in to appear to believe in equality."
Ms Lamont went on: ''While we will ask the rich to pay their fair share, the Nationalists tell us that would put Scotland at a disadvantage.
''Social injustice is what puts Scotland at its greatest disadvantage, and restoring the 50p tax rate will start to fight injustice.''
But she claimed Scotland has a ''Nationalist Government which refuses to reverse Tory tax cuts for millionaires, and a Nationalist Government which votes against workers on government contracts earning the living wage''.
She hit out: ''Forget talk of Indy lite - this Nationalist Government is Osborne Max.''
Ms Lamont said there was a "clear choice" facing voters in the independence referendum.
"There is the SNP - a party that has refused to endorse our policy of a 50p tax rate for the very wealthy. And there is Scottish Labour -a party that believes those with the broadest shoulders should contribute a fair share.
"The SNP - committed to slashing corporation taxes for bis business. Scottish Labour - a party that believes in investing in public services for the benefit of all."
A spokesperson for First Minister Alex Salmond said: "Scottish Labour and Johann Lamont appear obsessed with the SNP Government, and are still in denial about being out of office.
"They attack the SNP for honesty, but won't publish their own Cuts Commission. Will this mean the introduction of tuition fees, the end to free prescriptions, free personal care for the elderly, bus passes?
"If they want to be honest, they have to publish the results of their Cuts Commission, and tell us what social measures brought in by the SNP Government and previous administrations that they will scrap."
A Scottish Government spokesman responded to Ms Lamont's attack on plans to increase childcare, and said: "The Scottish Government increased free early learning and childcare provision for all three and four-year-olds from 412.5 hours to 475 hours-a-year in 2007.
"And last month Parliament backed our plans to increase this entitlement to 600 hours-a-year from this August and extend provision to vulnerable two-year-olds - giving parents additional support when they're seeking employment and maintaining that when they're successful.
"Ministers want to transform childcare through the opportunities and choices that are only available with having full control of Scotland's finances through independence and we have outlined, for the first time ever in the UK, a government blueprint for achieving universal childcare."