Mr Barr said the sale of $400 million in land – including the Northbourne public housing and other buildings on the road – was already factored into the budget. It must also be complete by mid 2019 to qualify for more than $60 million in incentive payments from the Commonwealth under its asset recycling scheme – designed to encourage states and territories to offload assets.

If the Liberals did not complete the building sales on time, they would miss out on the incentive payments and on the land revenue, creating a budget black hole, Mr Barr said.

Labor is set to give a $375 million lump sum to the private tram consortium when construction ends at the beginning of 2019, money that Labor says will come from the asset sales. Liberal Leader Jeremy Hanson has said he will redirect that money to a new building at the Canberra Hospital, costing $395 million.

But if Mr Coe slows down the Northbourne sales, the Liberals will have to find the hospital money elsewhere also.

Mr Coe said the Liberals would take a strategic approach, judging whether it was economically better to push ahead with the Northbourne sales or to sell the land more gradually, even if it meant missing out on the asset recycling money, he said.

"Because we're not desperately going ahead with this tram we can take a strategic approach to this and we can make sure we're getting the best price for these properties and we're not flooding the market with apartments," he said.

"That may well mean going ahead, but it may well mean that we're better off putting some of it on hold because having a fire sale at a time when there are so many apartments on the market is not necessarily in the best interests of Canberrans.

"There is an option on the table right now to sell these properties and that's fine, but it may well be that we're better off and the territory is better off choosing a different time frame."

Mr Coe said there was a "massive capital provision" already in the budget so there was no risk to the Liberals' hospital plans.

"Every decision we make will be based on what's in the best interests of the taxpayers rather than driven by the timeline of the consortium."

The Liberals have announced plans for two new bus lanes on Northbourne Avenue, with the extra 3.5 metres on either side carved from the median strip and the existing cycle lane. They also plan a bike path down the centre of the avenue, all the way from Gungahlin.

Mr Barr slammed the proposal, saying it would turn Northbourne Avenue into an "eight-lane gridlocked highway".

Asked about the bus lane proposal, the National Capital Authority said, "Any alternative proposal for transport options for this main avenue ... would be rigorously assessed in accordance with the provisions of the [National Capital] Plan ..

"The NCA supports improvements to Canberra's public transport system and any sustainable initiative that increases accessibility to central Canberra. The NCA considers that a complementary mix of transport modes that supports workers and visitors being able to easily move around the national capital should be the desired goal."

The Greens similarly attacked any plan to slow down the public housing renewal program.

"I can't see the point of slowing down the renewal of the Northbourne Avenue corridor," Greens Leader Shane Rattenbury said.

"There is a demand for housing in Canberra, we are seeing people interested in investing in that corridor, we are seeing businesses of course motivated by the presence of light rail," he said.

Mr Rattenbury said the Liberals' bus lane plan appeared likely to see trees along the median strip cut down, despite the opposition attacking light rail for doing the very same thing. "