The document comes after the United States, the European Union and Japan jointly filed a case in March at the World Trade Organization that challenged China’s restrictions on rare earth exports, which were imposed in 2006 and have been repeatedly tightened since then. The W.T.O. case argues that the export quotas and tariffs violate free trade rules by putting pressure on companies to move their factories to China if they want to tap China’s vast supply of rare earths.

Chinese officials have previously signaled that their defense in that case will be to use a provision of W.T.O. rules that allows export restrictions for environmental protection and the conservation of scarce natural resources. But they were quick to deny Wednesday that this had been their motive for releasing the white paper.

“The protection of the environment is never a pretext for gaining advantage or increasing economic returns,” Su Bo, a deputy minister of industry, said at a news conference in Beijing.

The white paper says China has only 23 percent of the world’s rare earth reserves and has already depleted the most accessible reserves. But the United States Geological Survey a year ago raised its estimate of Chinese rare earth reserves, to half the world’s supply, compared with a third of the world’s reserves.

Various local and provincial governments across China have announced numerous discoveries of large rare earth deposits in recent years, yet Chinese officials have scarcely changed official estimates for nationwide reserves, rare earth industry experts point out.