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.