The planned eco-towns have sparked a number of protests in England
Final approval will not be given to up to 10 "eco-towns" planned across England until early 2009 - three months later than originally forecast.
This is because a second consultation stage will run from September until December, the Department for Communities and Local Government said.
Fifteen sites were proposed but two have since dropped out of the running.
Some critics think the plans may not be scrutinised properly, while others fear local infrastructures will not cope.
There are strict criteria for the towns to ensure they meet certain environmental standards.
At least one person per household should be able to have a car-free journey to work, while the average home should be within a 10-minute walk of "frequent" buses or trains plus shops and other services.
Ford, West Sussex
Hanley Grange, Cambridgeshire
Imerys, nr St Austell, Cornwall
Leeds city region, West Yorkshire
Marston Vale, Bedfordshire
Middle Quinton, Warwickshire
Rossington, South Yorkshire
Weston Otmoor, Oxfordshire
Source: Department of Communities and Local Government
Each town will have between 5,000 and 20,000 properties and must be "zero-carbon" overall.
The Local Government Association has said it disapproved of the government's role in drawing up and approving such schemes.
It argued these powers should remain with councils as a way to ensure all proposals received "proper scrutiny".
The government has insisted applications will still go before local authorities and stressed eco-towns would have to comply with existing planning rules.
After the final decision on potential locations was made in early 2009, "each scheme will have to submit planning applications", said a spokesman for the Department for Communities and Local Government
The Financial Times reported on Tuesday that ministers were considering reducing the number of eco-towns but the DCLG spokesman added: "We have consistently said we are looking to build up to 10 eco-towns."
For the Conservatives, shadow housing minister Grant Shapps said: "The one certainty is that confusion reigns at the heart of Labour's controversial eco-town project.
"Local residents have been left in limbo as Caroline Flint performs U-turn on U-turn.
"She must set out a clear timetable for the eco-town project and end the uncertainty hanging over local communities."