The public is being asked to vote on more than 44,000 ideas for spending cuts submitted via a Treasury website.
The government said the "most promising" would be taken forward as part of the review of Whitehall budgets over the next four years.
Among the ideas displayed are cutting the number of deputy head teachers, merging all police forces and ending the painting of lines on country roads.
Visitors to The Spending Challenge website have until 31 August to vote.
This is ahead the government's spending review, expected to outline cuts of about 25% to most Whitehall departments, which will be published in October.
A Treasury spokesman said: "Visitors to the site will be asked to look through the ideas we've had and rate the ones they think have the most potential - helping us to identify the best ideas to be taken forward and investigated in further detail."
The 44,000 proposals were selected from more than 100,000 submitted.
The spending cuts programme is part of the Conservative-Liberal Democrat coalition government's efforts to reduce the £155bn budget deficit.