The plan is designed to succeed the Kyoto Protocol, which set binding targets on industrial countries to cut emissions of carbon dioxide and other gases believed to cause global warming, Kyodo News agency reported, citing unidentified Japanese and U.S. diplomatic officials.
"We must consider various steps, including setting numerical goals" to reduce greenhouse gas emissions, Japanese Prime Minister Shinzo Abe told reporters Tuesday.
U.S. President George W. Bush has already expressed support for Japan's proposal, which Tokyo will put forward at the G8 summit, the officials were quoted as saying.
Tokyo will suggest that the G8 countries - Britain, Canada, France, Germany, Italy, Japan, Russia and the United States - draw up plan details when Japan hosts a G8 meeting next year, Kyodo said.
It said Bush told Abe during talks in the U.S. last month that the U.S. leader was prepared to cooperate.
Japan's proposal is similar to reduction targets demanded by the European Union ahead of this year's G8 summit in Heiligendamm, Germany, where measures to counter global warming are expected to top the agenda.
Tokyo proposes developing new technologies to reduce emissions and taking other steps to halve emissions of carbon dioxide and other greenhouse gasses by 2050, Kyodo said.
U.N. officials have said they hope to launch negotiations on a post-Kyoto Protocol treaty at a climate change conference later this year in Bali, Indonesia. The protocol expires in 2012.