The ugly odor of protectionism is wafting through Washington, and President Obama should shut it off before it gets stronger.

The huge economic-stimulus bill he signed this week contains two provisions that seem, on the surface, to be saving American jobs. In fact, both clauses could be highly counterproductive, destroying far more jobs than they defend.

The first amendment, dubbed “Buy American,” requires construction projects financed under the bill to use only “iron, steel and manufactured goods ... produced in the United States.” Sounds good, particularly when the unemployment rate is 7.6 percent and headed higher. But what if other countries retaliate by imposing similar restrictions that cut off the flow of American exports?

Robert Zoellick, president of the World Bank, bluntly told The New York Times: “The ‘Buy American’ provision is very dangerous.”

The second clause restricts the ability of financial institutions receiving federal aid to hire foreigners holding H-1B visas, special permits for well-skilled and educated workers. These workers are absolutely essential for innovation and job creation. If we kick them out, other countries with a more enlightened view of the world economy will snap them up.

As economist Vivek Wadhwa of the Harvard Law School wrote recently in BusinessWeek: “We will scare away the world’s best and brightest who have always flocked to our shores. But the next Silicon Valley won’t be located in the U.S. It will likely be in Hyderabad or Shanghai.”

Fortunately, these provisions were watered down in the final version of the bill, but Obama has always been shaky on trade issues. During the campaign, he pandered openly to industrial unions that oppose free trade and even raised the possibility of renegotiating the North American Free Trade Agreement, a signature achievement of the last Democratic president, Bill Clinton.

Those were sleazy campaign tactics, designed to win votes in key states like Ohio and Michigan, but as political posturing they were not “very dangerous.” Now, as president, Obama has to look beyond short-term partisan benefit to long-term economic reality.

Here’s the problem: There’s a basic conflict between Obama’s core union supporters and that reality. By definition, labor leaders defend the status quo. They represent workers who have jobs now, even workers in aging industries using outmoded technologies.