First Minister Alex Salmond has given the strongest hint yet that Edinburgh's tram and airport rail link projects will be scrapped by the government.
He said a review by Scotland's spending watchdog had flagged up serious concerns over the costs of both.
Mr Salmond came under strong pressure from Labour and the Liberal Democrats to move ahead with the billion pound transport projects without delay.
But he said he would personally vote against the trams in parliament.
Auditor General Robert Black, who looked into the two projects, raised concerns about the airport rail link project, but was less critical of trams for the capital.
At first minister's question time, Labour leader Jack McConnell called for Mr Salmond to "have ambition for Scotland", demanding: "Will the first minister announce that he will stop delaying and announce that he will go ahead?"
Nicol Stephen, the Liberal Democrat leader and a former transport minister, said the auditor's assessment showed that the tram project appeared sound.
He added: "Scottish business is waiting, the projects are waiting, this parliament is waiting.
"Can we now have an honest statement from someone in this government about this important project?"
But the first minister pointed out the report's criticisms of the airport link, including that it was unlikely to be up and running by the 2011 target date.
"Under these circumstances, even Jack McConnell can't possibly be going to vote for that project," he said.
Mr Salmond went on to point out the auditor's concerns of a £48m shortfall for phase one of the trams project.
He went on: "Can I remind Jack McConnell that if we were, and I'll be voting against it, but if we were to start digging up the roads of Edinburgh for this project, its a bit like mastermind.
"If you start, you end up having to finish."
The SNP government, which is not convinced the two transport projects should go ahead despite being approved by the last parliament, is facing defeat in Holyrood next week over the issue.
But Mr Salmond, quoting the late Donald Dewar, indicated that the Scottish Executive had the power to ignore the will of parliament.