The Democrats are calling their alternative development plan "Thai Khem Khaeng 2020", the name the party gave to its economic stimulus scheme when it was in government in 2008-2011.
The opposition's intention is to show how it would spend the same amount of money over the same timeframe if it were in power, and in doing so highlight flaws in the government's scheme.
Mr Abhisit said the government's plan breaches the constitution and its investments could be handled more effectively if they were managed within the usual budgetary system rather than funded through a loans bill, as proposed.
Certain projects which the government intended handling alone should instead be joint ventures, he said.
The Democrats would spend the same amount of money over seven years as the government was proposing. However, the spending would cover a broader area, not just transport infrastructure.
He said the country also needed to prioritise other areas of development such as education, public health and water management.
The Democrat plan will also serve public needs better as it would cover all regions of the country equally and fairly, Mr Abhisit said.
The Northeast, for instance, often suffers droughts and studies have shown hundreds of billions of baht would be required to solve this problem, Mr Abhisit said. The government should spend some of the money on ending water shortages in the Northeast, he said.
"The government has often talked about poverty in Isan, but it chooses not to spend in this region," he said.
The government's high-speed train project would benefit only a few northeastern provinces as the line would only run as far as Nakhon Ratchasima, he said.
A Pheu Thai Party source said former prime minister Somchai Wongsawat has told MPs they must attend the debate on the borrowing bill.
He told a party meeting Tuesday each Pheu Thai MP faction head must ensure his MPs attend the vote on the third and final reading of the 2-trillion-baht borrowing bill on Saturday.
Pheu Thai deputy spokesman Anusorn Iamsa-ard said he was pleased to hear the Democrats are beginning to talk about development after having organised more than 60 public forums to defame the government.
Before the Democrats launch their new Thai Khem Khaeng plan, they had better let the public know about the corruption scandals that plagued their Thai Khem Khaeng stimulus scheme when the Democrats were in power more than two years ago, he said. He cited irregularities in the Public Health and Education ministries as examples.