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Democrat John Kerry (search) said Sunday that President Bush has turned his back on the American worker by allowing other countries to break trade deals negotiated with the United States and that as president he would put in place a "common-sense" effort to strengthen the bargaining and enforcement of such agreements.

"When I am president, we will never turn a blind eye to clear trade violations when American jobs are on the line," the presumptive Democratic presidential nominee told several thousand cheering Teamsters Union (search) leaders gathered for an annual convention.

Kerry sought to defuse tensions over trade, which emerged as an issue during the race for the nomination. He argued that while there are differences over trade policy, both he and union leaders agree trade deals must be enforced once they are sealed.

"This is not a philosophical question about free trade or protectionism," Kerry said. "It is just a common-sense question: Why aren't we enforcing our own laws on behalf of our own workers and businesses?"

Kerry said the nation's trade deficit stood at $500 billion largely because participating countries aren't required to improve labor standards and set environmental standards, making their products cheaper in this country and jeopardizing American jobs. In cases where those requirements exist, Bush isn't enforcing them, Kerry argued.

"This administration hasn't enforced our trade deals — I will," Kerry said. "I will because I know that when other countries walk all over our agreements, our companies and our workers can't compete."

As president, new agreements will include enforceable labor and environmental provisions, he said. He did warn the union leaders that he would continue to push for trade agreements, though he said he would reject a Central American trade deal Bush is likely to sign.

"I'm not a protectionist," said Kerry. "I don't think that most people who are reasonable expect that."

Teamsters President Jim Hoffa (search), meeting with reporters, conceded that Kerry has backed some trade deals the unions have fought, but said he's convinced Kerry has seen the error of his ways.

"I know he feels we have to change the way we do business," said Hoffa. "In the future he will have a different record."

In response, Bush campaign spokesman Steve Schmidt said: "John Kerry has long been an advocate of free-trade agreements. His rhetoric is at odds with his record."

Trade was a big issue during the fight for the Democratic nomination. Key Democratic constituencies, including labor, argue that pacts such as the North American Free Trade Agreement force U.S. workers to compete unfairly with cheap labor from overseas, where countries rarely enforce environmental and other standards.

The result, they argue, has been downward pressure on wages in this country, and incentives for companies to export jobs. Rep. Dick Gephardt, D-Mo., won overwhelming backing from those groups during the campaign for promising to end those trade deals if elected, including an enthusiastic endorsement from the Teamsters.

After Gephardt dropped out, the Teamsters moved quickly to endorse Kerry as he emerged as the front-runner. Gephardt was in the audience for Kerry's speech, but aides said the two did not meet during the convention. Kerry acknowledged him from the podium.

But Kerry has a nuanced position on trade. He supported NAFTA, other world trade agreements and elevated trade status with China. If elected president, the Massachusetts senator has said he would put all such agreements under a 120-day review and take unspecified "necessary steps" if they are found to be unfair to America. He also would require companies to notify workers and the government before moving jobs to other countries.

His challenge is to turn the Teamsters' endorsement into momentum for his challenge to Bush. The union, with 1.4 million members in the United States and Canada and a history of flirting with Republicans, has the foot soldiers and well-funded treasury to play heavily in the campaign. Kerry was meeting privately with union leaders before the speech.

Kerry's campaign theme this week is broadening opportunity — both economic and social — in this country. He heads to Topeka, Kan., on Monday to mark the 50th anniversary of the landmark Supreme Court decision that ended segregation in public schools. He also was touting his economic plan in Portland, Ore., with former rival Howard Dean.

Kerry also told the Teamsters that overhauling the nation's health care system would most help working families.

"We will make American businesses more competitive by reducing one of their biggest costs, health care," Kerry said. "It's costing families their life savings and it's costing businesses new jobs."