TV news legend Walter Cronkite is among the signatories

It appears as a high-level delegation from the European Union travels to Washington to try to keep the US from turning its back entirely on the Kyoto agreement.

The Australian Government, meanwhile, has showed some sympathy for the US position that developing countries must be included for an accord to be meaningful.

"You can't really have a comprehensive agreement unless you get the developing countries inside the tent," Australian Prime Minister John Howard said.

Momentous challenge

The open letter to President Bush stressed the importance of the environment.

"No challenge we face is more momentous than the threat of global climate change," the letter says.

"We urge you to develop a plan to reduce US production of greenhouse gases."

The message follows a storm of criticism from around the world at Washington's new position.

The letter signers include former US and Soviet leaders Jimmy Carter and Mikhail Gorbachev, financier George Soros, physicist Stephen Hawking and actor Harrison Ford.

The future of our children - and their children - depends on the resolve that you show

Letter to Bush

The other signatories are US Senator and former astronaut John Glenn, former newscaster Walter Cronkite, conservationist Jane Goodall, biologist Edward O Wilson and J Graig Venter, the president of Celera Genomics.

The letter says that, while the provisions of the Kyoto treaty were debatable, "the situation is becoming urgent, and it is time for consensus and action".

"There are many strategies for curbing greenhouse-gas emissions without slowing economic growth. In fact, the spread of advanced, cleaner technology is more of an economic opportunity than a peril.

George Bush has faced a storm of criticism

"The future of our children - and their children - depends on the resolve that you and other world leaders show," the letter said.

The president of the United Nations panel on global warming, Jan Pronk, has said he is planning to present new proposals to the US later this month on cutting greenhouse gases.

He was speaking on the last day of a meeting in Sweden of European environment ministers.

Monday's Time also publishes a poll showing that 75% Americans see global warming as a serious problem and 67% say Mr Bush should work towards a plan to deal with the problem.