Standing in for the Prime Minister at Commons question time, Ms Harman acknowledged the economic situation was "tough" and threatened to get "tougher".
She also told MPs: "The situation in the housing market is of grave cause for concern."
The Government had taken action and "will take more" to ensure stability, Ms Harman vowed.
But Liberal Democrat deputy leader Vince Cable said the Prime Minister should be doing more to tackle the housing "crisis".
Shadow foreign secretary William Hague offered Tory support to rush through legislation increasing saving depositors' protection before the summer recess.
Ms Harman shrugged off the Opposition's support, suggesting measures to ensure financial stability were already pencilled-in for the Queen's Speech in December and insisting ministers were keeping under close review the need to keep the "economy on track".
But Mr Cable said: "Do you acknowledge the severity of the crisis in the housing industry where leading private house builders are going bust, sacking 40 per cent of their workers and dragging down the banks because they've got an excess of unsold private houses.
"Will the Government build up its sensible, but pathetically small programme, for acquiring property, and give genuine freedom to councils and housing associations to acquire property in order to let it out to the 1.7 million people on housing waiting lists?"
Ms Harman replied: "I would agree with you. The situation in the housing market is of grave cause for concern. That is why the Government has taken action and will take more.
"But I think you would agree with me that the most important thing for housing for the future is that people can stay in their jobs - that employment remains high, and that inflation and interest rates remain low.
"That's what we intend to do."