Changes to building plans will put rare heathland birds in the south of England further at risk, the RSPB has said.
Nightjars, woodlarks and Dartford warblers are found on the heaths
Forty thousand homes are planned in Surrey, Hampshire and Berkshire, near the Thames Basin Heaths over 20 years.
The RSPB had backed plans from Natural England calling on developers to pay for alternative green space on any development within 5km of the heath.
An independent assessor has now said that developments of 10 houses or fewer should be exempt from the proposals.
The RSPB feared this would mean houses were built with no account for wildlife.
The regional assembly claims the move would deliver homes and protect the heaths.
The proposals are due to go before planning inspectors next month.
Planning manager for the South East England Regional Assembly, David Payne, said: "We welcome the assessor's positive suggestions in finding pragmatic solutions in the short and also longer term.
"There is still more work to do to deliver the recommendations which need commitment from all parties involved and up-front funding."
Chris Corrigan, RSPB South East regional director, said the assessor appeared to have "missed the point".
Rare bird species
"Excluding schemes of 10 dwellings or less would open the door to thousands of small, piecemeal developments.
"The cumulative effect of 40,000 homes would remain just the same and the bird populations will not suffer any less disturbance," he said.
Mr Corrigan said the heaths were home to rare bird species including the Dartford warbler, nightjar and woodlark.
Natural England, an agency set up by the government to champion the English countryside, said it believed the report provided a balanced view.
A spokesman said: "Natural England has argued that increasing the local population close to the heathland would threaten the survival of rare birds like the ground-nesting Dartford warbler, woodlark and nightingale.
"The assessor recognised the risk that large scale housing poses, and his report is an important step forward in developing appropriate solutions."
The building plans, covering the commuter belt towns of Guildford, Woking, Bracknell, Farnborough and Aldershot, were halted last year ahead of a public inquiry.