Senior party sources said the new leadership was eager to shed perceptions that it was "promising too much on public services" and wants to "get across the message" that Liberal Democrats can also be tough on public spending.
Matthew Taylor, the party's Treasury spokesman, is carrying out a "Comprehensive Spending Review" to define four or five key pledges on which the party will fight the next general election.
The main promises are likely to be on health, education, environmental tax and a change to the top rate of income tax to pay for better public services. "It is not just important to make four or five key promises but also to show how you would pay for them to convince voters that we are serious," one source said.
While the party is unlikely to drop its policy of "a penny on income tax", it will seek to counter government attacks of unrealistic spending commitments by linking the levy specifically to education.
The party plans to abolish Vehicle Excise Duty so that motorists would only have to pay tax when they use petrol.
"There are a lot of things our party wants to promise but we have to be realistic about what we can deliver if we want to be seen to be fit for government. For example, it would be great to abolish television licence fees for pensioners but that would cost hundreds of million and voters would not like it," an insider said.
Sources were playing down suggestions that they were "stealing New Labour's clothes" by using pledge cards.
"We have the difficult task of calling for more public spending without seeming irresponsible and too off-centre. We need to get across the message that we have our own ideas to deliver better public services and a credit- sized pledge card would be a good way of doing that at the next general election," one said.
Party strategists also stress that the battle for most seats will overwhelmingly be with the Conservatives in the South-west of England, not Labour.