US environmental policies have caused worldwide anger

Mr Powell was speaking at the opening of a major international environment conference in Washington, attended by delegates from about 30 countries.

He said many environmental issues are too big for individual governments to tackle, adding that partnerships between politicians, scientists and the private sector are essential to improve the environment.

However, the BBC's science correspondent Richard Black says some observers are concerned that calls for a unified system are no more than an excuse to delay action on global warming.

As well as the secretary of state, delegates are hearing speeches from a number of prominent American political figures, including Energy Secretary Spencer Abraham and presidential science adviser John Marburger.

Our correspondent says the heavyweight line-up illustrates the importance which the Bush administration attaches to the initiative.

Yet, he says, precisely what the proposed observation system would do is not entirely clear.

Excuse

The idea is to gather and collate environmental data from a range of sources, making something which scientists do already more systematic.

The US is asking for a 10-year commitment which will see the project gradually expand from the West into developing countries.

But there is no budget as yet, nor is it clear where the money is to come from.

There is concern among scientific and environmental groups that the Bush administration could use the observation system as an excuse for taking no action on climate change.