PORTLAND, Oregon: Senator John McCain sought to distance himself from President George W. Bush this week as he called for a mandatory limit on greenhouse gas emissions in the United States to combat climate change. McCain, in a speech on Monday at a wind power company, also pledged to work with the European Union to diplomatically engage China and India, two of the world's biggest polluters, if the nations refuse to participate in an international agreement to slow global warming. In the prepared text of his speech, e-mailed in advance to reporters, McCain went so far as to call for punitive tariffs against China and India if they evaded international standards on emissions, but he omitted the threat in his delivered remarks. Aides said that he had decided to soften his language because he thought he could be misinterpreted as being opposed to free trade, a central tenet of his campaign and Republican orthodoxy. In the U.S. South, a force to challenge the Republicans "I will not shirk the mantle of leadership that the United States bears," McCan said pointedly. "I will not permit eight long years to pass without serious action on serious challenges." In speeches on the campaign trail, McCain frequently highlights the threat of climate change in speeches, but he has a mixed record on the environment in the Senate. In recent years, he has pushed legislation to curb emissions that contribute to climate change, but he has missed votes on increasing fuel economy standards and has opposed tax breaks meant to encourage alternative energy. In his address on Monday, the presumptive Republican presidential nominee renewed his support for a "cap-and-trade" system in which power plants and other polluters could meet limits on greenhouse gases by either reducing emissions on their own or buying credits from more efficient producers. McCain's break with the Bush administration means that the three main presidential candidates have embraced swifter action to fight global warming. The two Democrats seeking their party's presidential nomination, Senators Barack Obama of Illinois and Hillary Rodham Clinton of New York, criticized the McCain plan as too timid. Leaders of a number of environmental groups were also sharply critical and noted his past Senate votes against incentives for energy conservation and alternative energy sources like wind and solar power. Other environmental advocates offered qualified praise for McCain, who was among the first in Congress to introduce legislation to address the carbon emissions that scientists blame for the warming of the planet. McCain said on Monday that the problem demanded urgent national and international action. "Instead of idly debating the precise extent of global warming, or the precise timeline of global warming, we need to deal with the central facts of rising temperatures, rising waters, and all the endless troubles that global warming will bring," he said at a Vestas wind turbine manufacturing plant in Oregon, where the environment is a central issue for voters. The senator's remarks were a clear criticism of Bush, who in his first term questioned the scientific basis for global warming and who has remained adamantly opposed to mandatory caps on emissions, which he says would be bad for the economy. The administration also rejected the Kyoto protocol, which limits emissions of heat-trapping gases. McCain's speech, a compilation and sharpening of many of his existing proposals, was most notable as a political document that sought to appeal to the independents he is wooing for November. It put him slightly to the right of center in the environmental debate. McCain is the only Republican presidential candidate this year to call for mandatory greenhouse gas limits, but his target for reducing emissions is lower than that of Clinton and Obama, and even lower than that in a bill proposed by Senator Joseph Lieberman of Connecticut, an independent, and Senator John Warner, Republican of Virginia. In his speech, McCain advocated cutting emissions 60 percent below 1990 levels by the year 2050; Clinton and Obama propose cutting them by 80 percent in the same time frame, while the Lieberman-Warner bill calls for a 70 per cent reduction. Scientists say reductions of that magnitude are needed to slow and then reverse production of the gases, chiefly carbon dioxide, that are heating the atmosphere and causing long-term climate changes. McCain said the United States must seek new, cleaner sources of energy to replace the burning of coal and oil, which produce the bulk of the greenhouse gases that are blamed for the warming of the planet. McCain's proposal in his prepared remarks to impose tariffs on industrializing countries like China and India is also made in the Lieberman-Warner bill and reflects concerns by both industry and labor in the United States and elsewhere in the industrialized world. It would mandate punitive duties on products from any country that did not participate in a global carbon-reduction system, to balance the lower cost of producing goods using dirty energy sources. Elisabeth Bumiller reported from Portland and John M. Broder from Washington. Kitty Bennett contributed reporting from Washington.