In his first meeting at the Western economic summit, President Reagan displayed drastic change in Washington by warning West German Chancellor Helmut Schmidt it would be risky for Bonn to buy natural gas shipped through the Soviet Union's new Siberian pipeline.

Neither Gerald Ford nor Jimmy Carter would have so directly confronted the imperious dean of Western summiteers. Nor was that the original intention of foreign policy bureaucrats preparing Reagan's strategy here. But on the Siberian pipeline, as on other key issues, politically appointed Reagan administration officials beat the bureaucrats.

The result was Reaganism at the summit. "The only thing we wanted to accomplish here," one senior presidential aide told us, "was showing that Ronald Reagan stood for something." They succeeded. If Reagan at home is accused of formulating no foreign policy, Reagan at Ottawa left no doubt where he stands.

Officials of the other industrialized democracies, who often complained Carter did not stand for anything, grumbled here that Reagan stands for too much. At Ottawa, they learned, as have congressional Democrats, that behind his warm personality and pleasing chatter, Reagan is rigidly ideological as no other American president has been.

The Ottawa summit came at an unpropitious time for Reagan, quite apart from interfering with his tax bill fight and coinciding with the newest Mideast crisis. His lone natural ally here, British Prime Minister Margaret Thatcher, is in political extremis. The accession of Socialist Francois Mitterrand to the French presidency pushes leftward the ideological balance of the industrialized democracies.

Under these conditions, the diplomatic bureaucracy in Washington advised Reagan to sweet-talk his way to leadership at Ottawa. Thus, early position papers for the summit urged accommodation toward the wish-lists of Bonn, Paris and Ottawa -- including the Siberian pipeline.

But the defense department intervened to insist that was not Ronald Reagan's policy. When Reagan arrived here, he immediately warned Schmidt of dependence on Soviet energy. The chancellor responded that the pipeline would supply only 5 to 10 percent of German energy needs. Reagan persisted, suggesting U.S. help in providing alternative energy sources -- coal and nuclear -- in place of Soviet gas.

This U.S. hard line in Ottawa came only after internal battling in Washington, and the same was true of Reagan's position on so-called North-South issues. State Department positions on aid to the underdeveloped Southern Hemisphere read suspiciously like Carter administration doctrine -- possibly because they were drafted mainly by Assistant Secretary of State Robert Hormats, who was a senior official in the Carter administration.

Non-Reaganaut Hormats encountered implacable opposition from Reaganauts in the Treasury and Office of Management and Budget. They switched the administration's position to opposition against a World Bank scheme for substantial U.S. financing of Third World energy development.

Another backstage battle was fought over the approach to the new French president. A first-draft briefing paper, prepared for Reagan by foreign policy bureaucrats, described Mitterrand as "a man of vision" whose views demand respect. The Reaganauts removed the offending language, and the paper's final version advised a courteous but arm's length approach to Mitterrand.

At issue was not the French president's personal merit but the danger of Reagan being trapped by Mitterrand and Canadian Prime Minister Pierre Trudeau in government projects to transfer resources from the developed North to the underdeveloped South. In his stiffly formal first meeting with Mitterrand, Reagan made clear his preference for the private sector in Southern development.

Thus, Reagan did more at Ottawa than answer complaints about U.S. interest rates and react to the Mideast. Reagan's positions set the boundaries of this summit, dooming full endorsement in the final communique of Trudeau's grandiose scheme for "global negotiations" to redistribute world wealth.

Other national leaders here did not like Reagan's intransigence any more than Carter's indecisiveness. "Reagan should remember what Harry Truman said: 'you can tell a man to go to hell, but you can't make him go,'" one European diplomat told us. "We have other options than blindly following the Americans." In fact, Reagan in Ottawa told nobody to "go to hell." But representing the industrial democracy best combining political stability, military power and economic health, he showed no hesitation in carrying Reaganism to the summit.