Aug. 11--Foreign trade has played a key role in defining the economic policies of the presidential contenders, and the issue's perceived impact on jobs and wages could be the determining factor in the election's outcome.

The private sector of the U.S. economy has shed jobs during each of the past eight months. The unemployment rate, which has increased by one percentage point nationally in the past year to 5.7 percent, has been rising even faster in many states.

In recent months, voters consistently have ranked the economy, including jobs, as the most important issue of the presidential campaign. With economic growth much slower today than a year ago, the jobs-related battle over trade may become the most decisive issue of the presidential election.

This is especially true in pivotal states such as Florida, Pennsylvania, Ohio, Michigan, Missouri, Minnesota and West Virginia, where the unemployment rate has increased significantly during the past year.

On the margin, the increasingly popular perception that soaring trade deficits have caused unemployment to rise could flip one or more states from President Bush's column in 2004 to Sen. Barack Obama's column in 2008.

On the other hand, the trade sector has become the principal factor that has kept U.S. economic growth positive in recent quarters.

"Over the past year, exports have accounted for two-thirds of our nation's economic growth," National Association of Manufacturers (NAM) chief economist David Huether told The Washington Times. "Rising exports are the brightest light for our economy right now."

"On trade, there is a stark distinction between the two candidates," said Sallie James, a policy analyst at the Cato Institute, which advocates unfettered trade.

Mr. Obama is "firmly in favor of government intervention," while Sen. John McCain "has an excellent and consistent record" supporting free trade, she said.

"In Obama's rhetoric, there are many signs that he understands the need for major surgery in U.S. trade policy," said Alan Tonelson of the U.S. Business and Industry Council, a national organization of small and medium-sized manufacturing firms.

By "adopting a blame-America-first trade policy," Mr. McCain "has no clue that countries sign trade deals with the United States to advance their own interests. He would be a dreadful bargainer," Mr. Tonelson said.

Both candidates agree that more needs to be done to strengthen the safety net for workers who lose their jobs because of trade. Each wants to help the transition of those workers to new jobs through better training and through reforms in the unemployment-insurance system or the trade-adjustment assistance program.

But they agree on little else.

Mr. Obama, the senator from Illinoisand the presumptive Democratic presidential nominee, captured his party's nomination after a fierce battle with Hillary Rodham Clinton over who would be a tougher negotiator with America's trading partners.

Mr. McCain, the senator from Arizona and the presumptive Republican presidential nominee, is a full-throated free-trader, who, after clinching his party's nomination, took international victory laps to Canada, Colombia and Mexico, extolling the mutual benefits of unfettered international commerce.

Disagreements between Mr. McCain and Mr. Obama over the costs and benefits of the North American Free Trade Agreement (NAFTA) have produced the most inflammatory rhetoric.

"I will make sure we renegotiate" NAFTA, Mr. Obama said in a debate before the Ohio primary. "I think we should use the hammer of a potential opt-out as leverage." Throughout the primary fight, Mr. Obama characterized NAFTA as "devastating" and a "big mistake."

"For all the successes of NAFTA, we have to defend it without equivocation in political debate because it is critical to the future of so many Canadian and American workers and businesses," Mr. McCain told the Economic Club of Canada in June. "Demanding unilateral changes and threatening to abrogate an agreement that has increased trade and prosperity is nothing more than retreating behind protectionist walls."

NAFTA, which passed Congress in bipartisan votes in 1993, became effective in 1994.