Conservative activists are praising President Bush's apparent decision to send Secretary of State Colin Powell to a U.N. conference on global ecology rather than attending the once-a-decade summit himself as his father did in 1992.

With the summit little more than two weeks away, there are no plans for Bush to go the conference, which conservatives have taken as a sign he will not attend.

"We applaud your decision not to attend the summit in person," said an Aug. 2 letter to Bush from Fred L. Smith Jr., president of the Competitive Enterprise Institute, and 30 other conservative activists who support Bush.

The letter warns of likely widespread anti-U.S. sentiment among the participants at the World Summit on Sustainable Development being held Aug. 26 through Sept. 4 in Johannesburg, South Africa. Other signers include Paul M. Weyrich of Coalitions for America, Grover Norquist of Americans for Tax Reform and David A. Keene of the American Conservative Union.

"Your presence would only help to publicize and make more credible their various anti-freedom, anti-people, anti-globalization and anti-Western agendas," they wrote Bush. "We also strongly support your opposition to signing new international environmental treaties or creating new international environmental organizations at the Johannesburg summit."

The White House has been silent so far about who will lead the U.S. delegation to the summit. Administration officials say an announcement will come soon, but Powell is expected to attend.

This is the fourth summit in four decades where world leaders and environmentalists have gathered to address the environmental costs of feeding, clothing and housing the Earth's growing population.

For environmentalists, the series of talks reached a height in 1992 at Rio de Janeiro, Brazil, when Bush's father, George H.W. Bush, then the president, was among 110 world leaders who agreed to tackle problems in forestry, biodiversity and climate change.

The conservatives say those talks were a mistake for the elder Bush, one that his son is now wise to avoid.

"Why would you go to a party when they want to throw pies at you?" Smith said in an interview. "The fortunate thing is when 40,000 goofies get together, not much happens."

In 1972 at Stockholm and in 1982 at Nairobi, each of the U.S. delegations was led by the chairman of the White House Council on Environmental Quality.

The current chairman, James Connaughton, has not said whether he will attend. More than 100 world leaders -- either the head of state or a minister-level representative -- have announced they will be at the summit.

Many among them share a deep concern about the state of the world's ecological systems, and some have said they also worry about a lack of leadership and lackluster U.S. support for global approaches.

Summit leaders say they will try to solidify commitments made over the past year to open markets to developing countries and increase financing to them. They also cite challenges such as 2 billion people living on $2 or less a day, more burning of fossil fuels blamed for climate change and damage to a quarter of the world's coral reefs.

Connaughton said whoever represents the United States will emphasize both the U.S. commitment to creating lasting partnerships and also the idea that each nation bears responsibility for its own development.

"It doesn't mean they go it alone. But each nation has to take that task onto itself to look at sustainability," he said recently.

Some environmental leaders view this year's summit as a last, best chance to convert high hopes into deeds.

"There is a real sense of urgency," U.N. Undersecretary-General Nitin Desai, who will chair the summit, told reporters this week. "In many cases we are talking about slipping back."

In the weeks leading up to the summit, Desai has campaigned to sow seeds of hope while also warning that disappointment will only confirm widespread pessimism about the world's ability to deal with what he says is a growing crisis.

"We will be endangering all of the things we have achieved and we will not have another chance," he told summit leaders at the Brazilian Embassy in Washington earlier this month. "There is no major global event planned beyond Johannesburg which allow us to retrieve lost ground. This is it."

Gus Speth, dean of Yale University's School of Forestry and Environmental Studies, said world leaders are running out of time because the world economy is projected to double in size every 25 years.

"We have squandered more than 20 years on these global-scale issues and this period we're in is truly our last chance to get it right," Speth said.

The uncertainty about U.S. participation reflects deeper questions in the environmental community about Bush's approach to global challenges in the wake of his rejection last year of the Kyoto climate treaty.

"People around the world are seriously concerned that the Bush administration is undermining the World Summit instead of working with other countries to benefit everyone," Sierra Club director Michael Dorsey said.