Back then, once-arcane concerns about climate change and deforestation had finally grabbed the world's attention, leading to a global treaty on biodiversity and decisions that cleared the way for the Kyoto agreement on greenhouse gases.

Now, though, the minds of global leaders are elsewhere.

Instead of clean energy, food, the oceans and other topics scheduled for debate at Rio+20, as the summit is known, political focus is attuned to a teetering Europe, turmoil in the Middle East and a presidential campaign in the United States.

Although more than 50,000 visitors are expected in Rio de Janeiro by the end of the three-day event starting Wednesday, few concrete results are expected from the summit.

At best, officials could agree on clarity for proposed "sustainable development goals," a loose tripod of economic, environmental and social objectives that proponents believe could help guide global development.

So dim are the prospects that Brazil's lead negotiator in the run-up warned that the summit risked being "held hostage" by other priorities.

"We are here to think about the long term," said Luiz Alberto Figueiredo, an undersecretary at Brazil's Foreign Ministry, "not crises that may be overcome in one or two years."

But hopes have long been low for the summit, officially called the United Nations Conference on Sustainable Development.

U.S. President Barack Obama said months ago he would not attend. The leaders of Germany and Britain are staying home, too.

Many of those who do come likely will be focused on matters discussed Monday and Tuesday at the Group of 20 meeting in Mexico, where leaders of the world's major economies are debating the global economic downturn.

Still, some reject the notion that gains cannot be made in Rio. Former U.S. President Bill Clinton, on a conference call about climate issues, called Rio+20 an important "working conference."

"Everybody has made all the speeches they can make," Clinton said on Monday, predicting that delegations from the United States and Europe would still be productive despite the absence of major heads of state. His wife, Secretary of State Hillary Clinton, is leading the U.S. delegation.

FOCUS ON DEVELOPMENT, NOT ENVIRONMENT

Brazil, a prominent voice in the environmental debate as home to the world's biggest rainforest, for months has been tempering the hopes of environmentalists seeking a repeat of the 1992 summit. After a decade-long economic boom, Brazil and other big emerging nations refuse to put environmental concerns ahead of their own drive for growth.

"The summit can't just be about the environment," Antonio Patriota, Brazil's foreign minister, said in a recent interview. "It has to be about development."

Environmentalists say the planet is no better off now than in 1992. With continued melting of polar icecaps, record greenhouse emissions last year and a global population on track to grow to at least 9 billion by 2050, according to U.N. projections, existing policies have done little to assuage human demands on the global ecosystem, they argue.

A key difference from two decades ago is that the Earth Summit was the culmination of years of negotiations to fashion some of the first international environmental policies ever created. This meeting, by contrast, is the beginning of a process to establish so-called "sustainable development goals."

When established, the goals are expected to build upon a current round of objectives, known as the millennium goals, which U.N. members agreed to pursue at least through 2015. Those objectives include eradicating hunger and extreme poverty, improving access to education and reducing child mortality.

LITTLE PROGRESS IN PRE-SUMMIT NEGOTIATIONS

U.N. negotiations are slow-moving processes that require finding common ground among 193 member countries and bridging huge gulfs in priorities between the developed world and emerging markets. And the sustainable development goals, while still being defined, are built around three vague issues that mean different things to different countries: economic development, social inclusion and the environment.

"The specific objectives differ globally, between and within societies," Jeffrey Sachs, the Columbia University economist, wrote in a recent essay, noting no consensus on priorities.

Delegations hammering out a declaration for Rio+20 in recent days have not gotten far on building that consensus. After plans to wrap up a draft by the weekend failed, delegations are now scrambling to get something together by the time their leaders descend upon Rio mid-week.

"We see a lopsided victory of weak words over action words," said Lasse Gustavsson, leader of the World Wildlife Fund's delegation at the summit.

As with long-simmering differences over greenhouse emissions, use of the seas and other divisive issues, negotiators are haggling over wording and implications the text could have on the entrenched positions of rich countries, developing nations and regional blocs.

The United States, for instance, opposes the inclusion of a phrase favored by emerging markets.

The phrase, "common but differentiated responsibilities," reflects what developing nations consider their right to catch up with the rich world and as such have more leeway on emissions and other environmental concerns. China, for instance, is now the world's largest emitter of greenhouse gases but it is still far behind developed nations in per-capita prosperity.

The timing of the summit also means countries are reluctant to consider financial commitments. Talk of the creation of a $30 billion fund for development goals quickly faded.

"We dont think there is any one fund that can solve these problems," Kerri-Ann Jones, an assistant U.S. secretary of state, said in a briefing last week.

RIO BRACES FOR GRIDLOCK

In Brazil, organizers hope that at least the logistics of the event come off successfully.

As the country gears up to host the 2014 World Cup and the 2016 Olympics, it is scrambling to upgrade highways, airports, stadiums, and other facilities needed to accommodate the expected crush of visitors. With millions of new cars on the road after a decade of prosperity, cities like Rio and Sao Paulo are routinely crippled by traffic and minor emergencies that strain old and rickety infrastructure.

In recent days, Rio residents have been bracing for gridlock once authorities close lanes, slow air traffic and beef up security to make way for expected leaders including Russian President Vladimir Putin, Chinese Prime Minister Wen Jiabao, and Iranian President Mahmoud Ahmadinejad.

Meanwhile, the already colorful city has seen a splash of summit-related demonstrations by activists.

On Sunday, demonstrators on Copacabana beach unfurled a giant "trillion dollar bill" to protest fossil fuel subsidies by governments. On Tuesday, demonstrators are scheduled to cart a replica of a military tank, made of bread, into a slum to protest the precedence of defense budgets over social spending.

• A Permanent Economic Emergency