Cancelling the tram contract later this year would cost between $220 million and $280 million, Capital Metro Minister Simon Corbell said, slamming the Liberals' promise to scrap the contract as "reckless and lunatic".
And Capital Metro head Emma Thomas said all 14 trams had already been ordered. Track-laying, stop-building and other permanent work would not begin until late in the year, when detailed design was complete. Capital Metro was expected to lodge a detailed construction program in mid July.
The actual pay-out figure if the tram was scrapped would be based on how much the tram consortium had spent and committed to spend when the contract was cancelled.
Mr Corbell said the estimate had been calculated by the government, using the formula set out in the termination clause in the contract with the Pacific Partnership-led consortium, which will build and operate the tram.
Transport Canberra acting deputy director-general Duncan Edghill said the figure was based on the consortium's spending of about $20 million to $30 million a month in the five months between the contract being signed and the election, as well as project debt and other costs related to financing.
Mr Corbell attacked the Liberals' promise to tear up the contract as "mad" and "confirmation of the lunacy of [the Liberal] position", with ongoing consequences as companies factored in the possibility of cancellation in their prices for future contracts.
Pressed by the Liberals' Alistair Coe about how he had calculated the figure, he said the government had not asked the consortium itself for projected spending because if the contract was terminated the territory and consortium would effectively be in dispute.
The cancellation clause was not unusual, but it was "no cheap exit clause; this is a very costly clause to exercise", he said.
The figure came as federal Liberal polling suggests at least one in five Canberrans are so opposed to the Gungahlin tram that they are prepared to change their vote in the federal election.
The outcome to the federal election has no direct impact on Canberra's light rail project, which is being delivered by the ACT government.
But the Liberals are nevertheless using the project in the final days of their federal campaign, hoping to swing some votes in Saturday's election and damage Katy Gallagher's bid for re-election.
From Monday night, the party was using the tram in signs, direct mailouts and online advertisements.
The material urges votes to "Send a message on light rail: put Labor and Greens last", and reminds voters that as chief minister, Ms Gallagher signed a power-sharing agreement with the Greens to deliver light rail.
The Liberal telephone poll early in June found a substantial block of opposition to the light rail project, with 48 per cent saying they opposed the project. Thirty-three per cent supported it, and 19 per cent declared themselves neutral.
Opposition is substantially stronger in the electorate of Canberra, which covers the southern side of the city, than in the northern electorate of Fenner. In Canberra, 54 per cent of voters are opposed, and in Fenner, 43 per cent are opposed.
Among people opposed to the tram, 20 per cent said the tram was a vote-changing issue in the federal election and a further 10 per cent said it was "possibly" a vote changer. Seventy per cent said it was not.
Among Labor voters, 17 per cent of opponents said it was a vote-changer for them; 68 per cent said not. Among Green voters opposed to the tram, just five per cent said it was a vote changing issue for them.
Senator Zed Seselja said the poll showed Canberrans were angry at light rail, and not interested in a "Greens-Labor vanity project".
ACT Liberal Alistair Coe said the result "reflects what we are hearing on the ground all across of Canberra".
The poll was done by the Sexton Marketing Group on June 7-8 among 600 voters. The Canberra Times has been given results for only two questions and no other context or questions.
The ACT Liberals will also campaign hard on the tram in the lead-up to the October territory election, saying they will halt the project if they win government.