OTTAWA - Finance Minister Jim Flaherty said Thursday he considers it imperative that the government restrain the growth of public pensions, although he stopped short of calling them unsustainable.

Flaherty made clear that changes are coming to the Old Age Security program that pays an average $500 a month to lower-income Canadians upon turning 65, and that he will outline the government's thinking in the upcoming budget.

"This is not an issue that can be ignored unless we want to put at risk the fiscal track of the country, which would be a mistake," he told reporters Thursday on a conference call from Tel Aviv, where he has been visiting for most of the week.

"The research we have, both within and outside government, has shown us for some time that the demographic challenge will bring substantial pressure on the long-term sustainability of these programs."

The opposition parties and some experts have been critical of the government for presenting the issue as a clear-cut case of unsustainability.

Ottawa estimates the cost of OAS will rise from $36 billion in 2010 to $108 billion in 2030, while the number of taxpayers for every senior declines from four-to-one to two-to-one.