The public "does not yet know if it can trust" the Conservatives on the economy and public services, shadow Treasury spokesman Philip Hammond has said.
Philip Hammond made his comments at a fringe meeting
Mr Hammond said that meant it was vital the party did not make "unfunded upfront commitments".
He made his comments at fringe meeting at the Tories' conference in Blackpool.
Shadow chancellor George Osborne earlier pledged to cut inheritance tax and stamp duty ahead of a possible autumn general election.
But Mr Hammond's comments could raise questions about whether the Conservatives are ready to fight a campaign which could get underway in the next few days.
Asked whether a campaign as short as four weeks offered enough time to turn things around, Mr Hammond said: "Well I think we've started.
"As we start to deliver specific policies, people will see, not just the general commitments, but the very specific commitments that we are making."
Mr Hammond told the Politia fringe meeting: "We have to recognise that in 1997, the Labour Party set out its agenda recognising that it had a problem, that the public did not trust it on the management of the economy.
"We have to recognise that in 2007 the public does not yet know whether it can trust the Conservative Party on the management of the economy.
"That is why we must be very clear. We must put stability first and not make unfunded upfront commitments.
"We have another problem as well. The public does not know that it can trust the Conservatives on the administration of public services."
He said a Conservative government had to ensure that as the economy grew it "shared the proceeds of growth".