WASHINGTON — President Obama yesterday imposed punitive tariffs on all car and light truck tires entering the United States from China in a decision that could anger the strategically important Asian powerhouse but placate union supporters important to his health care push at home.

Obama had until Sept. 17 — next week — to accept, reject or modify a U.S. International Trade Commission ruling that a rising tide of Chinese tires into the U.S. hurts American producers. A powerful union, United Steelworkers, blames the increase for the loss of thousands of American jobs.

The federal trade panel recommended a 55 percent tariff in the first year, 45 percent in the second year and 35 percent in the third year. Obama settled on slightly lower penalties — an extra 35 percent in the first year, 30 percent in the second, and 25 percent in the third.

By taking "this unprecedented action, the Obama administration is now at odds with its own public statements about refraining from increasing tariffs above current levels," said Vic DeIorio, executive vice president, GITI Tire (U.S.), the largest maker of tires in China.

The decision comes as U.S. officials are working with the Chinese and other nations to plan an economic summit of the Group of 20 leading rich and developing nations in Pittsburgh, to be held Sept. 24 to 25. China will be a major presence at the meeting, and the United States will be eager to show it supports free trade.

Many of the nearly two dozen world leaders Obama is hosting have made strong statements critical of countries that protect their key industries. Obama, too, has spoken out strongly against protectionism, and other countries will view his decision on tires as a test of that stance. Governments around the world have suggested the United States talks tough against protectionism only when its own industries are not threatened. U.S. rhetoric on free trade also has been questioned because of a "Buy American" provision in the U.S. stimulus package.