He emphasised that key departments such as education and employment, health and culture, media and sport should seek best value rather than the lowest costs in procuring buildings.
Foster said: "The importance of the political initiative in favour of quality in architecture cannot be overstressed. An architect can only advocate, he has not direct power and his advocacy can, or cannot, be acted on.
"That is why government has to make sure that it is understood and acted on by those procuring the proposed new public infrastructure.
"Government departments must understand that if they spend an extra 15% on the building in the first place, energy savings, the reduction in pollution and the increase in staff productivity over its 25-year life will pay for itself many times over."
Foster urged government to take a holistic view of urban regeneration as a mix of individual buildings, infrastructure and activities.
Lord Foster also said quality was the key factor in the tall buildings debate: "There is an obsession with the height of buildings. It is not how high, but how high is the quality?"
Foster said there was a place for clusters of towers in London's Docklands and the City but questioned the suitability of other locations: "It is not surprising that an intense area should express itself as clusters. Towers are not invaders from Mars which will appear on every street corner."
In another speech at the Bartlett School of Architecture Foster defended the green credentials of tall buildings, which he said could prove more environment-friendly than large-footprint deep-plan "groundscrapers".
He said: "Tall buildings don't threaten the essential greenery of London as a city. Filling a site with a groundscraper will not arouse political opposition but it will not leave any room for public space."
