OTTAWA, Dec 3 (Reuters) - Canadian Prime Minister Stephen Harper will address the nation on Wednesday night as speculation heightens that he will ask for a temporary suspension of Parliament to try to prevent the opposition from taking power.

Governor General Michaelle Jean, who will play a key role in the political crisis gripping the country, is due back from a foreign trip several hours before the prime minister speaks.

Harper, whose Conservatives were reelected with a minority government on Oct. 14, is expected to say that a plan by the three opposition parties to bring down the government and install a coalition government is illegitimate.

A leading option he is considering is asking Jean to suspend Parliament at least until his government can present a budget with new measures to stimulate the economy in late January.

Jean is the representative in Canada of Queen Elizabeth, the country’s head of state, and must weigh competing constitutional arguments on whether to grant such a request or a possible later Conservative request to call a new election.

She is returning to Ottawa at 3 p.m. (2000 GMT) from Europe, and Harper’s televised address is set for 7 p.m.

Harper aides would not say whether he would meet Jean this afternoon.

The main opposition Liberal Party, the separatist Bloc Quebecois and the left-leaning New Democratic Party signed an agreement on Monday to try to replace the Conservatives with a Liberal-NDP government supported by the Bloc.

To do so they would first have to defeat the government in a confidence vote in Parliament scheduled for next Monday evening. That would be prevented for now if Parliament is suspended. (Reporting by Randall Palmer; editing by Peter Galloway)