WASHINGTON (AP) -President Barack Obama heads to Canada on Thursday with a decidedly pro-trade message, hoping to reassure an enormously valuable partner that the U.S. is not pulling back even as it enforces new “Buy American” language and considers renegotiating the 1994 North American Free Trade Agreement.

In his first foreign trip as president, Obama will meet with Canadian Prime Minister Stephen Harper in Ottawa, the Canadian capital. The relationship between their countries is vital: No country takes part in as much daily trade with the U.S. or exports as much oil to the U.S. as Canada does.

Yet the new American president has stirred up some nervousness north of the border by pledging to renegotiate NAFTA, which links the U.S., Canada and Mexico, to get better labor and environmental standards. When he was seeking the Democratic presidential nomination a year ago, Obama said “we should use the hammer of a potential opt-out as leverage to ensure that we actually get labor and environmental standards that are enforced.”

The Obama team now, though, is choosing softer language. A renegotiation on standards could spiral into a broader, and perhaps messier, reopening of NAFTA. Right now, the three nations have a big, lucrative trade zone.

“Obviously, given the delicate state of the global economy, (Obama) wants to make clear to Prime Minister Harper and to all of our trading partners that this is no time for anybody to give the impression that somehow we are interested in less – rather than more – trade,” said Denis McDonough, Obama’s senior foreign policy adviser, said Tuesday.

“That’s the message that he’ll underscore.”

Obama maintains that the worker and environmental standards in NAFTA, now considered side agreements, could be strengthened and made part of the main pact. McDonough said Obama will use this visit with Harper, and conversations with Mexican President Felipe Calderon, to make that point.

Meanwhile, Canadian worries have subsided somewhat over the “Buy American” clause wrapped into the giant economic stimulus bill Obama signed Tuesday.

It requires that U.S. iron, steel and other manufactured goods be used for public buildings and other public projects paid under the bill. But the final language makes clear that the policy must not violate U.S. obligations under existing international trade agreements, including NAFTA.

Obama’s quick trip to Canada is to be dominated by the economy, trade, energy, the environment and the war in Afghanistan.

Setting a tone, Obama told a Canadian news organization Tuesday that the United States will seek a more comprehensive, diplomatic approach to Afghanistan, where the U.S. has been engaged in war since 2001.

“I am absolutely convinced that you cannot solve the problem of Afghanistan, the Taliban, the spread of extremism in that region solely through military means,” the president said in a White House interview with Toronto-based Canadian Broadcasting Corp.

“We’re going to have to use diplomacy,” Obama said. “We’re going to have to use development. And my hope is that in conversations I have with Prime Minister Harper, that he and I end up seeing the importance of a comprehensive strategy, and one that ultimately the people of Canada can support, as well as that the American people can support.”

The president made those comments hours before adding some 17,000 U.S. troops for the flagging war in Afghanistan, his first significant move to change the course of a conflict that his closest military advisers have warned the United States is not winning.

Although the Afghanistan conflict is overshadowed in the U.S. by the war in Iraq, the Afghan war is a deeply sensitive matter in Canada.

Canada is planning to pull its forces out of the country’s volatile south by 2011, with diminishing support among its people to keep troops there.

AP-ES-02-17-09 1842EST