Talks Open on Treaty to Cut Global Warming : Environment: Negotiators at U.N. are under pressure to reach accord for signing at Rio summit in June.

UNITED NATIONS — In an 11th-hour effort, diplomats from more than 100 countries opened the final round of negotiations here Thursday to draft an unprecedented treaty to reduce global warming.

Negotiators are under intense pressure to produce a draft treaty by the end of next week. If they do not succeed, they warn, it is unlikely that an accord will be ready for signing by world leaders when they convene in June in Rio de Janeiro for a major conference on the environment and development.

At the same time, chief U.S. negotiator Robert Reinstein said that the outcome of the talks would probably affect a decision by President Bush on whether to attend the Rio conference, known informally as the “Earth Summit.” There are growing signs in Washington that Bush will attend the summit, but the White House has announced no decision.

In pleading for a spirit of compromise, conference chairman Jean Ripert of France told delegates: “We’re coming into the final stretch. The finish line is in sight.” Ripert conceded, however, that delegates face a formidable task in reconciling conflicting national views on how to go about reducing emissions and financing the effort. “I hope we can all arrive there together,” he said.

But even as negotiators assembled for the make-or-break session, there was little indication that the United States--the most conspicuous holdout in acceding to a firm cap on emissions of global warming gases by the year 2000--would agree.

Reinstein told reporters that the United States would be “painting (itself) into a corner” if it signed a treaty to hold emissions to 1990 levels by the year 2000 only to find out later that the target could not be met without “sacrificing” economic growth.

The European Community has called for such a cap, and Britain announced for the first time Thursday that it would support the European position. The British previously had called for a 2005 deadline.

The United States announced last week that it could reduce its annual output of carbon dioxide--the principal greenhouse gas--by 125 million to 200 million metric tons by the year 2000. But even with that cut, overall U.S. emissions in the year 2000 would be from 1% to 6% higher than they are today. The United States accounts for one-fourth of all human-caused carbon dioxide emissions in the world.

In a move to break the stalemate, Ripert unveiled a proposed compromise as a basis for negotiations during the next week.

Ripert called for “a spirit of compromise” and urged delegates to take a “long-term perspective” that would allow emission reductions to be phased in gradually. He also said the treaty should be flexible enough to take into account new information and circumstances. But he did not elaborate during the public session.

Earlier, Reinstein told reporters, there had been “intense consultations” among a number of countries prior to Thursday’s session.

“There have been considerations of elements that might be involved in some kind of bridge between opposing positions,” he said, adding that he was not free to elaborate.

An hour before the negotiations began, protesters from the Greenpeace environmental group forced security officers to seal off the United Nations grounds. Some demonstrators climbed flagpoles while others chained themselves beneath a truck at one U.N. entrance.

Two others joined in the protest by using ropes to rappel from the top of the 40-story U.N. Plaza Hotel nearby, then partially unfurling a banner. The stunt caused even the usually impassive New Yorkers to gawk. Police pulled the pair in through a hotel window after they had lowered themselves 12 stories.

In London on Thursday, three Greenpeace activists climbed on scaffolding around a tower of Parliament and hung a banner saying “Now Save The Ozone Layer.”

Two of the three remained suspended from the 336-foot-tall Victoria Tower for about two hours before complying with police orders to descend on a mechanical hoist. The third demonstrator climbed down the scaffolding to the ground.

Scotland Yard said all three were arrested.