THE cabinet will rule out a 'build now, pay later' plan for a Dublin airport metro line drawn up by the embattled Rail Procurement Agency (RPA), raising doubts about the future of the metro project.

Transport minister Seamus Brennan is due to bring proposals on metro to government in the next couple of weeks. These proposals have yet to be finalised, but there is now waning enthusiasm within government for the RPA option.

The Department of Finance is expected to be particularly hostile to the plan, which envisages the metro being funded through a public private partnership with a price tag of ?350m a year for 20 to 30 years. While there would be no initial exposure to the exchequer, the final bill would be up to seven times the ?1bn estimate put on the project by Madrid expert Professor Manuel Melis.

In the Dáil last week, finance minister Charlie McCreevy was keen to stress that no decision had been made about building the metro.

Given the problems that have beset the Luas project, ministers are understood to be reluctant to hand over the building of metro to the RPA.

They are still shocked at the RPA's initial cost estimate of ?4.8bn for the airport line, which would have made it the most expensive metro project anywhere in the world.

There is also deep scepticism within government about the suggestion that the RPA would run the project in tandem with experts from Madrid. This is seen as impractical and a recipe for serious tensions on the project.

Given the high cost of building metro, there is deep concern that, if the project goes wrong, the impact on the public finances could be disastrous.

If the decision is taken not to go with the RPA proposal, the government is left with two options. It can adopt a 'do nothing' approach, whereby metro is effectively put on hold. Or, it can look to develop the metro without the involvement of the RPA as advocated by the opposition parties. It is understood that little or no consideration has been given to the latter option.

The 'do nothing' approach is regarded as almost unthinkable for economic and PR reasons. There is general agreement that a metro is highly desirable to ensure that the capital city ? the centre of economic activity ? does not grind to a halt.

Failure to back the metro project could also put a further dent in the government's popularity as the idea has captured the public's imagination.

In contrast, a positive decision on metro could be a vote-winner come the next general election. There is also a belief that three years ago the cabinet made the wrong decision in not dumping Luas in favour of metro. At the time, Luas was a relatively popular option with the public and media and there were worries about a public backlash if the project was scrapped.

The Department of Transport is anticipating a "battle" at cabinet over metro. However, as of now, the department is still backing the RPA plan and stressing that the agency largely inherited the Luas project and that a beefedup RPA, procuring the best international expertise, is the best option for metro.

However, Brennan himself has had a difficult relationship with the RPA over the Luas, metro and, more recently, how best to deal with the Luas/Red Cow roundabout issue.