Federal departments and agencies are being told to start tightening their belts as the Liberal government looks for ways to pay for its latest budget promises while taking off political heat.

Tuesday's federal budget contains billions of dollars in planned new spending measures for the health-care system, clean-energy infrastructure and other priorities.

Yet hidden among the promised new investments are plans to cut in some areas.

That includes a new review aimed at cutting spending by about three per cent across all federal departments and agencies, with a few exceptions, such as for the military.

The government is also responding to criticism about the amount of money spent on outside firms such as McKinsey & Company by ordering cuts to spending on consultants as well as government travel.

Billions of dollars in previously announced programs and projects are also being redirected to other areas, though officials did not provide a list of what is being affected.