The Tories would tax people less than Labour if they won the next general election, Iain Duncan Smith has said.
Iain Duncan Smith is confident about the Conservatives' prospects
The party leader claimed the goal would be achieved by cutting "bureaucracy and waste" in public services.
On the eve of the Tory conference he said he had never been more confident that he would become prime minister.
But a Times opinion poll suggests voters do not have faith in the Tory leadership team, and think they are out of touch with ordinary people.
When asked about Mr Duncan Smith's tax pledge, shadow chancellor Michael Howard said it did not necessarily mean taxes would be cut under a Tory government.
He told BBC Radio 4's Today programme that they "hope" and "plan" for this to happen, but could make no promises at this stage.
But he claimed tax bills under a Tory government would be lower, suggesting Labour would certainly impose further tax rises in the future.
The Tories have long asserted they are a lower tax party than Labour.
In an interview with the Daily Telegraph Mr Duncan Smith said the aim would be achieved without hitting frontline services.
"This government has ramped up taxes 60 times and we will be a lower tax government than Labour," he said.
"We plan to cut taxes by cutting bureaucracy and waste."
Mr Howard told Today: "I want to cut taxes, I hope to cut taxes, I plan to cut taxes.
But he added: "I can't yet make any firm promises, partly because we haven't completed our work on identifying the waste that we can cut, and partly because we don't know the state of the economy at the time of the election."
Chief Secretary to the Treasury Paul Boateng took his comments as evidence of a Tory split over tax.
He said: "First Iain Duncan Smith makes a promise to cut taxes, then Michael Howard says he can't guarantee to cut taxes.
"It is clear you still can't trust the party that ruined the economy in the early 1990s, and introduced the biggest tax rise in history, on tax.
"But while they can't guarantee tax cuts, we know that they have guaranteed not just to cut spending on the health service, but also to privatise it."
BBC political correspondent John Andrew said there appeared to have been some presentational muddle, and that the tax plan was simply a firming up of existing policy.
The Tory leader told the Telegraph a government under his control would not be committed to Labour's spending plans on health and education.
This was because he did not believe the government had presented meaningful proposals for public sector reform.
Asked if he would match Chancellor Gordon Brown's public spending projections, he said: "We will not commit ourselves to their spending plans because we think they've been badly set on the basis of no reform."
The Blackpool conference will also see the publication of a document forming the basis of the party's election manifesto.
Called 'Trusting People - a Fair Deal for Everyone', it will back subsidies for private health and education.
It will also propose scrapping
university top-up fees, an extra 40,000 police and an annual asylum-seekers quota.
'Honest and principled'
Mr Duncan Smith remains bullish about his position.
He told the Telegraph: "I'll be prime minister after the next election. I've never felt more confident in my life about this."
But the Times poll suggested a majority did not believe that the Tories had improved since losing power in 1997.
The party scored a rating of minus 51% on whether it had a good leadership team, minus 41% on understanding the way British people live today and minus 33% on caring about the needy.
But, in the Populus survey of 1,012 it scored better than Labour on being "honest and principled", being united and focusing attention on the country's real priorities.