Mr Alexander set out the Lib Dem's "four big steps to a fairer Britain"
The Liberal Democrats have said they will fight the general election with a stripped-back manifesto.
Danny Alexander, charged with drawing up the party's election manifesto, said it would contain only the essentials.
The Inverness MP told the party's Scottish conference in Perth it would be "short, direct and to the point."
Mr Alexander also warned some of the Lib Dems' long-term commitments would have to wait if the party won power, because of spending pressures.
Mr Alexander, chief of staff to UK Lib Dem leader Nick Clegg, told the conference: "The Liberal Democrat manifesto will be short, direct and to the point.
"We have stripped away everything that is not essential because the country cannot afford it."
Mr Alexander said difficult decisions had been taken, adding: "I know it is not easy to put on hold some long-standing commitments that we won't be able to deliver in the next parliament."
That meant, he said, the dropping of pledges on free child care, free personal care for the elderly in England and Wales and a citizens' pension.
Mr Alexander outlined "four big steps to a fairer Britain" - fair taxes, a fair start for all children at school, a rebalanced green economy and "clean, open politics".
Policies included, he said, making the first £10,000 of earnings tax-free - paid for by closing tax loopholes exploited by the wealthy - spending more on schools and "breaking up the banks so they can never again wreck the economy".
Plans drawn up by the Calman Commission to give the Scottish Parliament more powers would also be implemented immediately.
Mr Alexander said the party was "poised to make gains across the land" in the forthcoming UK election.