Redford told reporters her government would need to hike spending by four per cent over last year's budget of $41 billion just to keep up with population growth plus inflation.
"The severe downturn in resource revenues has made even that (four per cent) level of growth unsustainable," said Redford.
"In tomorrow's budget our spending will be far below — far below — estimated population growth and inflation.
"With the province growing as quickly as Alberta, that does mean a significant measure of restraint, and it means that we do have to make some very difficult choices."
Redford has said the budget will be a watershed document that will lay out long-term plans for spending and saving, and take the first step to getting the province off its day-to-day dependence on mercurial oil and gas revenues.
A pipeline bottleneck to customers in the United States, coupled with a glut of oil from North Dakota, has been depressing the price of Alberta's signature oilsands crude.
Redford has said the price drop could cut in half the $13 billion the province had hoped to bring in from non-renewable resources during the 2013-14 fiscal year.
Her government, which has prided itself on being debt-free, has begun borrowing to pay for big-ticket infrastructure projects like twinning the highway to the oilsands hub of Fort McMurray.
Redford and Finance Minister Doug Horner have also recently hedged on promises to balance the books on the day-to-day operating side.
The premier has said all will become clear when Horner unveils the budget Thursday afternoon.
Wildrose Leader Danielle Smith has criticized Redford for record spending when times were good, but said she is cautiously optimistic that the new mantra of lean spending represents a foundational shift.
"I'm not quite sure that I believe the premier on that, but we'll see because we've been calling for this for years," said Smith.
NDP Leader Brian Mason said even a hold-the-line budget in a growing province is bad news for Alberta families.
"I'm expecting that we're going to see cuts to basic services, including health and education. I think we're going to see layoffs of employees," said Mason.
Liberal Leader Raj Sherman said the province needs to return to a progressive tax system rather than the current 10 per cent flat tax.
Sherman said the flat tax means the wealthy are not paying their fair share. He chastised Redford for further pursuing "trickle-down" economics by refusing to alter the tax structure in this budget.
"Redford today is doubling down on trickle down," said Sherman.
Also Wednesday, Redford did an about-face and allowed the Canadian Taxpayers Federation into the pre-budget briefings.
The briefings allow the media, opposition members, and other stakeholders to ask questions about the budget before it's tabled in the house in order to better understand it.
However, the taxpayers federation was told this year that there was no space in the briefing room for them, prompting Smith to extend the group an invitation as a one-day employee of their caucus.
Redford told reporters that her decision to let the federation in was a bi-partisan one. She said Wildrose member Ian Donovan told her Tuesday night that the watchdog group should be allowed in, and she agreed.
"I (told the federation), 'If this important to you, fine. I don't want this to be a distraction from the budget, so fill your boots,'" said Redford.
Smith said Redford's change of heart came from bad publicity suggesting her government was being petty.
"It's pretty outrageous that (Redford) has to be arm-twisted, and pushed and pressed to do the right thing. They never should have been excluded in the first place," said Smith.
Horner said the government found space for the Federation by opening up a second briefing room. He denied the move to ban the group was payback.
Last year the federation publicized research that showed an all-party legislature committee was getting paid thousands of dollars a year while never meeting.
The so-called "no-meet committee" scandal dogged Redford's party in the first week of last year's election campaign, prompting her to issue an order for all the committee money from her caucus to be paid back.
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