HONG KONG  China unexpectedly increased pressure Sunday on the United States in a widening trade dispute, taking the first steps toward imposing tariffs on American exports of automotive products and chicken meat in retaliation for President Obama’s decision late Friday to levy tariffs on tires from China.

The Chinese government’s strong countermove followed a weekend of nationalistic vitriol against the United States on Chinese Web sites in response to the tire tariff. “The U.S. is shameless!” said one posting, while another called on the Chinese government to sell all of its huge holdings of Treasury bonds.

The impact of the dispute extends well beyond tires, chickens and cars. Both governments are facing domestic pressure to take a tougher stand against the other on economic issues. But the trade battle increases political tensions between the two nations even as they try to work together to revive the global economy and combat mutual security threats, like the nuclear ambitions of Iran and North Korea.

Mr. Obama’s decision to impose a tariff of up to 35 percent on Chinese tires is a signal that he plans to deliver on his promise to labor unions that he would more strictly enforce trade laws, especially against China, which has become the world’s factory while the United States has lost millions of manufacturing jobs. The trade deficit with China was a record $268 billion in 2008.