The motoring and services body has turned up the heat as the State Government works towards an electricity privatisation plan it says will net $15 billion for infrastructure.

Armed with that money, as well as part of the Federal Government's $21.7 billion budget surplus, the NRMA says the State Government would no longer have excuses as to why the much-needed link could not be built.

NRMA deputy president and southern area director Michael Tynan said the case for the extension from Loftus to St Peters was overwhelming: economic, environmental, safety and tourism benefits as well as the fact commuting workers could spend more time with their families.

The extension would mean motorists, who now travel through congested roads in southern Sydney, could reduce their fuel consumption for that part of the journey.

NRMA plans for the road also include a bus lane to cut down on car usage.

"With the recently announced record federal budget surplus our community has never been in a better position to build this critical road," Mr Tynan said. "This road needs to be built - if we delay it further it will become more expensive."

The Mercury understands Keira MP David Campbell and Heathcote MP Paul McLeay have made a strong case for the extension inside the party room but have met opposition from the likes of Roads Minister Eric Roozendaal, who prefers other projects.

Despite the F6 being identified for future transport use in crucial State Government planning documents - the Metropolitan Strategy and State Infrastructure Strategy, the latter which maps out targets leading to 2016 - Mr Roozendaal says there are no plans for road development along the corridor.

"The NSW Government's position regarding the F6 transport corridor remains unchanged," the minister's spokeswoman said.

"The Iemma government is committed to working co-operatively with the Rudd government to improve the road network across NSW."