When Ronald Reagan announced his candidacy for president Nov. 11, 1979, virtually the only new idea in his speech was a proposal for a "North American Accord" designed to forge closer relations among the United States, Canada and Mexico.

Reagan said that as president he would "be willing to invite each of our neighbors to send a special representative to our government to sit in on high-level planning sessions with us."

It was a deliberately vague proposal, intended by the campaign manager at the time, John Sears, to show that Reagan had some new ideas. And it received a predictably cool reaction from government leaders in Canada and Mexico, who weren't eager to have the question of hemispheric relations become a central issue in the presidential campaign.

Now, as president, Reagan says he reamins committed to the idea, still vague, of an accord that would tie the three nations closer together.

He will have his first chance to explore this proposition with Canadians this week when he travels to Ottawa for a two-day visit that will include public and private meetings with Prime Minister Pierre Trudeau on Tuesday and an address to the House of Commons the next day.

In advance of this, Reagan is learning that the specifics of international cooperation with a friendly but touchy neighbor require far more attention to detail than his broad-gauged campaign comments.

The Canadians, with a government that has moved left as the United States was turning right, are concerned about continuity of commitments on a range of issues, including air pollution, energy, water projects and world relations.

Two long-pending issues, a treaty resolving fishing rights off the East Coast and U.S. participation in a pending Alaska gas pipeline that would traverse Canada, probably would head any Canadian agenda.

Canada has been building its section of the pipeline, while the United States has yet to do even preliminary work. And the Canadians are worried about the prospective impact of Reagan's gas deregulation plan on the sales of pipeline gas, which will inevitably be expensive after its long haul from Alaska.

Reagan is eager to show that he seeks true cooperation with Canada. In advance of the visit, he sent a letter to Chairman Charles H. Percy (R-Ill.) of the Senate Foreign Relations Committee, asking an urgent meeting of the committee to approve a treaty that would disputed maritime boundaries in the Gulf of Maine to binding arbitration.

The letter asked that the boundary treaty be ratified without an accompanying fisheries agreement.

"After examining the matter, it is clear to me the fishery treaty cannot be ratified in a form that would be acceptable to Canada," the letter said. "There seems to be no controversy in realtion to the boundary settlement treaty. Therefore, I believe it would be best to uncouple the two treaties and proceed with the ratification of the boundary settlement treaty."

While Reagan in his letter took issue with Canadian fishing rights claims, he also said he would order the Coast Guard not to enforce U.S. laws in maritime areas claimed by Canada.

The fishing rights dispute centers on the harvest of scallops on Georges Bank. Canadian fishermen claim three-fourths of the catch on the basis of historical division, and U.S. fishermen have been ignoring this claim.

The U.S. Senate, heeding the arguments of its domestic fishing industry, has refused to ratify the treaty, and the prospect is that Canadian fishing will resume unless the issue is resolved in the next few weeks.

Canadians also seek assurance of continued U.S. willingness to participate in cleaning up the Great Lakes and seek Reagan's view on a 1980 memorandum of intent in which both governments agreed to develop an agreement to reduce air pollution. Canada is particularly concerned about the harmful effects of acid rain originating in the United States.

Reagan is expected to assure the Canadian government that he intends to live up to this agreement despite his well-publicized support for a relaxation of environmental controls.

Emphasizing the underlying friendliness of U.S.-Canadian relations, both countries are likely to use the trip to announce continuation of a North American Air Defense Command (NORAD) agreement that expires May 12.

More than anything, the visit will provide an opportunity for Reagan and Trudeau to size each other up and, if all goes well, establish a pattern for future cooperation.

It is doubtful if there are two leaders of stature in the western world who are less alike in philosophy and temperament.

But polls show Reagan's popularity soaring in Canada since the election, as it has in the United States, and both leaders have enough persistent internal problems to make friendly relations politically desirable.

Trudeau faces real problems of separatism, not only in Quebec, but in the western provinces, which are unrepresented in Trudeau's Liberal government and which generally favor closer relations with the United States and approve of Reagan's North American accord.

Reagan will try to explain carefully the U.S. policy toward El Salvador, to which Trudeau has expressed public objections. Even as Trudeau did so, however, some Canadian sources said they were pleased that high U.S. government officials privately had talked to them in advance about U.S. policy -- something Canadians complain that President Carter neglected to do before launching his boycott of the 1980 Olympics in retaliation for the Soviet invasion of Afghanistan.

No American president had visited Canada since President Nixon in 1972. A scheduled Carter visit was canceled because of the Iranian hostage crisis, and some Canadians expressed private misgivings that it was never rescheduled.

Trudeau, however, personally liked Carter. It remains to be seen whether he will develop similar warm feelings for Reagan.