But the complainants argued that the restrictions were inconsistent with China’s obligations under the rules of the World Trade Organization, which it joined in 2001, because they were handled “in a manner that is not uniform, impartial, reasonable, or transparent,” distorting the market in favor of China’s domestic industry.

Critics also argued that despite the claims of environmental protection, China was using its monopoly to create a cost advantage for companies operating within its borders; because the price was lower for domestic users, the arrangement induced foreign companies to set up shop in China to be competitive, creating local jobs and transferring technology.

The panel ruled against China’s arguments on all counts. While it did not rule that nations may not impose quotas to protect scarce resources, it argued that once a commodity was extracted from the ground it should be treated in accordance with the global rules.

World trade rules do not prohibit export taxes. But the agreement China signed with other countries when it joined the W.T.O. allowed for only a limited number of such duties and did not include rare earths, the panel noted.

Beijing now has about two months to appeal the case, as do the complainants if they think the outcome is not entirely in their favor. Any challenge would be heard by the Appellate Body, the World Trade Organization’s permanent appeals tribunal.

China’s statement Wednesday said Beijing was “assessing the panel report and will follow the W.T.O. dispute settlement procedures to settle this dispute.” It gave no indication of whether it planned to appeal.

If China does appeal, the Appellate Body would probably make a final ruling by the end of July, said James Bacchus, a former chairman of the tribunal who is not involved in the current case. Mr. Bacchus said it was unlikely that the Appellate Body’s ruling would be significantly different, and that the judges there can rule only on matters of legal principle, not on the panel’s findings of fact.