United States attempts to persuade Australia to join a proposed Sinai peace-keeping force have a slimmer chance of success now that Canada apparently has refused to join such a force.
Canada will not become involved in the proposed force because it does not have United Nations support, diplomatic sources say.
Australian Prime Minister Malcolm Fraser, now on a North American tour, will hold talks this week with Canadian Prime Minister Pierre Trudeau. The prime ministers are expected to discuss the Sinai force.
Australian political observers say Canada's decision to stay out of Sinai will make it much more difficult for Australia to participate in the force. They note it will not be easy to justify Australian involvement if Canada, a middle-ranking power of similar size and with close ties to the US, prefers not to become involved.
The force is being convened by the United States, Egypt, and Israel to supervise Israeli withdrawal from Sinai under the provisions of the Camp David peace treaty. The three nations have agreed to set up a multinational force, but the agreement still needs formal approval of the Egyptian and Israeli parliaments.
While in Mexico City last week, Mr. Fraser said his government will make no immediate decision on Australian participation. He said there would be no decision during his Washington visit this week, and remarked that under no circumstances will Australia be pressured into making a hasty assessment. His statement followed reports that US Secretary of State Alexander M. Haig Jr. had indicated Australia would probably make a judgment within a week.
Canberra observers suggest the Australian government is increasingly dubious about committing troops to the force.
Australia's main opposition party, the Labor Party, has opposed involvement for the same reason Canada opposes it: absence of United Nations backing. A smaller party, the centrist Australian Democrats, hold a similar view.
Mr. Fraser emphasized in Mexico City that no announcement was likely, "even for a while after I get back to Australia." This caution is viewed in Canberra as a measure of reservation about the merits of commitment to US foreign policy.
Some supporters of the National Country Party -- junior partner in the governing coalition with Mr. Fraser's Liberal Party -- fear involvement in the force would put at risk valuable wheat and la mb export markets in Arab nations.