Both the Environmental Protection Agency and Conservation Commission knocked back the proposal on grounds that the development could harm the island's fragile ecoculture and rare plant and wildlife species.

The responses, and that of the Department of Industry and Resources, were prompted after Gorgon developer ChevronTexaco put up a detailed development plan that included using Barrow Island as a base for processing infrastructure.

The tone of the agency responses needs to be read alongside pointed comments made by Chevron Australia's chief executive, Jay Johnson, last week that: "there is no fall back after Barrow, this is the only option."

Johnson was referring to suggestions that the Gorgon field should be developed without the use of Barrow Island. Johnson dismissed the idea saying that locating the plant on WA's mainland would add $1 billion to the project's cost, ruling out any hope of it being viable.

Jim Limerick, the Chair of the Standing Interagency Committee of Chief Executive Officers (SIAC), which is responsible for coordinating the whole-of-government strategic assessment process, said the government had not yet made a decision on the proposed development, or guaranteed any outcome on the use of Barrow Island by Gorgon.

"However, as there is no established process in WA to strategically assess the environmental, social and economic costs and benefits of significant development proposals such as this, we have sought advice from a range of sources, including public comments, to assist the government," he said.

"The Environmental Protection Authority and the Conservation Commission have advised they consider that access to Barrow Island is not compatible with the island's very significant environmental and conservation values. As requested, those agencies have also recommended appropriate conditions for such access, should the government agree to it."

Dr Limerick said the current process does not replace future assessments under the Environmental Protection Act and the Commonwealth Environmental Protection and Biodiversity Conservation Act, should the Government give in-principle approval.

The agency responses now go out for six weeks for public comment. After that the State Cabinet must decide whether to give Chevron in-principle approval to use Barrow Island or not.