The agreement reached during a visit by Romanian President Traian Basescu comes ahead of the Eastern European nation's accession to the European Union which would make it more difficult to obtain credits.

The Kyoto Protocol, the first-ever international law on global warming, requires industrialized nations to slash emissions of greenhouse gas.

But nations can sell their excess credits to another country, such as by setting up environmentally friendly technology.

"The size of excess emission credits that East European countries have is enormous. Japan plans to reach similar agreements with other East European countries as well," a foreign ministry official said after Basescu's talks with Prime Minister Junichiro Koizumi.

The Japanese government worries that if East European countries join the European Union, former communist countries will be deprived of their right of sell emissions due to complex EU trading rules.

Romania has won provisional approval to enter the EU in 2007.

"Both Romania and Japan are aware of the time limit of 2007, when Romania is scheduled to become a member of the EU," an environmental ministry official said.

The agreement Thursday will be followed by discussions on how Japan will obtain the credits from Romania.

Romania is estimated to have about 400 million tons of excess emission rights, which is far above Japan's need for 100 million tons of emission rights through Kyoto's program known as "joint implementation," according to the environmental ministry official.

"But the agreement with Romania is not enough -- one JI program such as renewing an old oil-fired power plant only can earn hundreds of thousands of tons," said the official.

The United States walked away from Kyoto as it regards the treaty as unfairly punishing the world's biggest economy by not requiring emission cuts by developing countries such as China and India.

Japan backs the treaty reached in its ancient capital but businesses have been critical of government threats to force compliance by imposing taxes against emissions.

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