A leaked federal government advisory board report that does not make a case for the contentious Perth Freight Link is a major embarrassment to the Liberals, the opposition says.
The leaked report by Regional Development Australia instead describes an outer harbour further south at Kwinana as a "nation building" project that requires strong government intervention.
The federal government has committed to funding almost 63 per cent of the three-stage Perth Freight Link, with the first two phases estimated at $1.9 billion.
Labor says there is no logic in pushing ahead with the link as it will lead to the century-old Fremantle Port, which the report says will reach full capacity between 2025 and 2035.
The state government estimated last year that construction would be complete by 2019, but the time frame has slipped because of blunders in the environmental approvals process.
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Federal Labor MP Alannah MacTiernan says pursuing the unpopular project is "completely irresponsible".
"If we don't proceed with developing the outer harbour and making sure that we have got efficient port infrastructure ... this will damage our economy into the long term," Ms MacTiernan told reporters on Sunday.
"This will be selling WA short.
"It is outrageous. This is not the way to go."
WA minister John Day said the primary federal government body providing advice on the link was Infrastructure Australia, which was in strong support.
"The Freight Link project is needed now," Mr Day said.
"We agree that there will at some stage need to be an outer harbour built, but that wouldn't be open and operating until at least 10 years, even if we were to give an in-principle decision to go ahead today.
"There is long-term planning being done but that does not obviate the need to deal with issues as they arise today."
Mr Day singled out reducing congestion on Leach Highway as the main reason to push ahead with the link.
The project is controversial because part of it will cut through the Beeliar wetlands, a tunnel will require homes to be bulldozed, and the final stage has not yet been decided upon, prompting opponents to label it a "road to nowhere".
