The US Republican party is changing tactics on the environment, avoiding "frightening" phrases such as global warming, after a confidential party memo warned that it is the domestic issue on which George Bush is most vulnerable.

The memo, by the leading Republican consultant Frank Luntz, concedes the party has "lost the environmental communications battle" and urges its politicians to encourage the public in the view that there is no scientific consensus on the dangers of greenhouse gases.

"The scientific debate is closing [against us] but not yet closed. There is still a window of opportunity to challenge the science," Mr Luntz writes in the memo, obtained by the Environmental Working Group, a Washington-based campaigning organisation.

"Voters believe that there is no consensus about global warming within the scientific community. Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly.

"Therefore, you need to continue to make the lack of scientific certainty a primary issue in the debate."

The phrase "global warming" should be abandoned in favour of "climate change", Mr Luntz says, and the party should describe its policies as "conservationist" instead of "environmentalist", because "most people" think environmentalists are "extremists" who indulge in "some pretty bizarre behaviour... that turns off many voters".

Words such as "common sense" should be used, with pro-business arguments avoided wherever possible.

The environment, the memo says, "is probably the single issue on which Republicans in general - and President Bush in particular - are most vulnerable".

A Republican source, speaking on condition of anonymity, said party strategists agreed with Mr Luntz's conclusion that "many Americans believe Republicans do not care about the environment".

The popular image is that they are "in the pockets of corporate fat cats who rub their hands together and chuckle manically [sic] as they plot to pollute America for fun and profit", Mr Luntz adds.

The phrase "global warming" appeared frequently in President Bush's speeches in 2001, but decreased to almost nothing during 2002, when the memo was produced.

Environmentalists have accused the party and oil companies of helping to promulgate the view that serious doubt remains about the effects of global warming.

Last week, a panel of experts appointed at the Bush administration's request to analyse the president's climate change strategy found that it lacked "vision, executable goals, clear timetables and criteria for measuring progress".

"Rather than focusing on the things we don't know, it's almost as if parts of the plan were written by people who are totally unfamiliar with where ecosystems science is coming from," panel member William Schlesinger told the Guardian.

Mr Luntz urges Republicans to "emphasise the importance of 'acting only with all the facts in hand'", in line with the White House position that mandatory restrictions on emissions, as required by the Kyoto protocol, should not be countenanced until further research is undertaken.

The memo singles out as a major strategic failure the incoming Bush administration's response to Bill Clinton's last-minute executive order reducing the permitted level of arsenic in drinking water from 50 parts per billion to 10 parts per billion.

The new administration put the plan on hold, prompting "the biggest public relations misfire of President Bush's first year in office", Mr Luntz writes. The perception was that Mr Bush "was actively putting in more arsenic in the water".

"A compelling story, even if factually inaccurate, can be more emotionally compelling than a dry recitation of the truth," Mr Luntz notes in the memo.