Speaking at a Conservative party caucus meeting, Harper echoed projections from the Bank of Canada a day earlier that said the country's economic progress was being impaired by international factors, namely slow U.S. recession recovery and the European debt crises.
"Circumstances demand that we listen carefully to Canadians and that we be flexible when necessary," Harper said.
Parliament resumes Sept. 19 from summer recess.
The Conservatives' two top agenda items are cutting government spending among all departments by as much as 10 percent, as well as an omnibus crime bill, the Canadian Broadcasting Corp. said.
The federal Conservatives have a majority in Parliament, although there are six provincial and territorial elections in coming months that will bring out regional political sentiments that aren't in line with Harper's Conservatives.
The official parliamentary opposition New Democratic Party is under temporary leadership after the death of Jack Layton last month. The Liberal party is also under temporary leadership after the March election that voted out its leader and many members of Parliament.