WASHINGTON (Reuters) - The United States on Tuesday set preliminary duties of less than 5 percent on solar panels from China it said were unfairly subsidized, two sources familiar with the decision said.

The U.S. Commerce Department determined Chinese solar cell and panel manufacturers received government subsidies worth 2.90 percent to 4.73 percent of the value of their product, the sources said.

Importers will have to post bonds or cash deposits based on the preliminary countervailing duty rates while the department continues its investigation. The Commerce Department will issue a preliminary decision on antidumping duty rates in May.

The decision could disappoint SolarWorld Industries America, the U.S. arm of Germany's largest solar manufacturer and the head of a U.S. industry coalition which filed a petition last year asking for import relief.

The group says U.S. production of solar cells and panels is threatened by Chinese competitors that receive generous government subsidies and "dump" their products in the United States at unfairly low prices.

The Commerce Department set a preliminary duty of 2.90 percent on SunTech Power Holdings, the world's biggest producer of photovoltaic solar panels, and a preliminary duty of 4.73 percent on Trina Solar, another major Chinese producer, the two sources said. All Chinese solar producers and exporters received a rate of 3.59 percent.

Analysts had expected duties in the range of 20 percent to 30 percent.

Shares in Suntech, which had sunk earlier in the day, quickly jumped after the report to trade 5.4 percent higher, while Trina Solar shares rallied 8.1 percent and Yingli Green Energy shares surged more than 10 percent.

The United States imported $2.8 billion worth of solar cells and panels from China in 2011, up sharply from about $1.2 billion in 2010, according to industry estimates.

(Reporting By Doug Palmer and Matt Daily in New York; Editing by Anthony Boadle)