In an apparent setback for environmentalists worldwide, top leaders of the Group of Eight major nations meeting in Okinawa next month are unlikely to set a specific target date for putting into effect the Kyoto Protocol on curbing global warming.

In a joint declaration to be issued at the end of the three-day Okinawa summit, which starts on July 21, the G8 leaders will simply pledge to make the 1997 protocol effective as soon as possible, government sources said Thursday.

The global environment is expected to be a major topic of discussion at the Okinawa summit.

The sources said that while Japan and European G8 members want to see the Kyoto Protocol become effective by 2002, the U.S. and Canada remain adamantly opposed to setting any specific target date.

Under such circumstances, the G8 leaders should avoid repeating the sharp confrontation that their environmental ministers had over the issue in early April, the sources said.

If Japan and Europe insist on including a target date in the summit declaration, it would “give an impression that the G8 countries are in disarray,” one government source said. “That would not be a good thing.”

But a failure to set a specific target date for putting the Kyoto Protocol into effect would likely draw criticism from environmental groups as well as developing countries, which claim global warming should be primarily blamed on industrialized countries.

At the end of their three-day talks in Otsu, Shiga Prefecture, in April, the G8 environmental ministers issued a joint communique in which they confirmed their “commitment to ensure that results achieved at COP6 (in The Hague in November) help promote the ratification and entry into force of the Kyoto Protocol as soon as possible.”

“For most countries, this means no later than 2002,” it said.

The wording of the joint communique was the result of a compromise among the G8 countries.

The G8 countries are Canada, Britain, Germany, France, Italy, Japan, Russia and the United States.

The Kyoto Protocol was adopted at COP3 — the third Conference of Parties to the United Nations Framework Convention on Climate Change — in Kyoto at the end of 1997. The U.N. convention was signed at the Earth Summit in Rio de Janeiro in 1992.

The Kyoto Protocol sets legally binding targets for industrialized countries to reduce the emissions of carbon dioxide and some other greenhouse gases that are widely blamed for global warming, by a total of 5.2 percent between 2008 and 2012 from 1990 levels.

It specifically requires Japan to make a 6 percent cut in such emissions, the U.S. a 7 percent cut and the 15-nation European Union an 8 percent cut.

At COP3, delegates from more than 150 countries agreed to introduce schemes, including the emissions trade mechanism, aimed at helping industrialized countries to achieve their targets.

Under the emissions trade mechanism, industrialized countries that face difficulties in achieving their greenhouse gas-reduction targets would buy the emission rights from other countries that can afford to make deeper cuts in gas emissions.

But details of the schemes have not yet been worked out. Largely because of the absence of agreements on the schemes, no industrialized country has ratified the Kyoto Protocol.

It is widely believed that agreements on the emissions trade mechanism and other schemes will have to be reached at COP6 to make the Kyoto Protocol effective by 2002, as demanded by Japan and Europe.

In the face of strong pressure from the Republican-dominated Congress, the U.S. administration of President Bill Clinton has consistently insisted that major developing countries also make a “meaningful participation” in efforts to slash the emissions of greenhouse gases before the U.S. ratifies the protocol.

The U.S. is the world’s largest producer of greenhouse gases, accounting for nearly a quarter of the total emission volume.