For months foreign leaders and environmentalists have wondered whether President Obama would attend a landmark U.N. conference slated for late June, known as the “Rio+20 Summit.”

The answer remains unknown..

In a conference call with reporters Tuesday, U.S. special envoy on climate change Todd Stern said that when it comes to the prospect of Obama attending the U.N. Conference on Sustainable Development in Rio de Janeiro, “I don’t have any understanding that the president has any intention of going.”

Administration officials, who asked not to be identified because the question concerned a future scheduling matter, said Tuesday that a final decision had not been made. A White House official wrote in an e-mail that when it came to Obama’s possible attendance at Rio+20, “I don’t have any scheduling announcements at this time.”

More than 120 presidents and prime ministers from around the globe—including the leaders of China, India and Germany—have announced they’ll attend a high-level segment of the gathering, scheduled for June 20-22.

The meeting, which marks the 20th anniversary of the 1992 Rio Earth Summit, has major symbolic significance even though it remains unclear whether it will produce many concrete results. Two decades ago President George H.W. Bush attended the initial summit, which produced major environmental agreements including the U.N. Framework Convention on Climate Change as well as the U.N. Convention on Biodiversity.

Jacob Scherr, global strategy and advocacy director for the Natural Resources Defense Council, said he and others hope Obama will show up.

“We’ve known for a long time the president’s been undecided. We’re still hopeful that the administration will continue to consider whether the president will go,” he said in an interview. “We think it would be a real tragedy if the U.S. is missing in this effort to try to put the world on a more sustainable path.”

George W. Bush chose not to attend the U.N. Earth Summit in 2002, which took place in Johannesberg. Scherr said that if Obama chose to skip the event, “It will be noticed by the rest of the world.”

Just last week, Obama joined other Latin American heads of state in issuing a joint communique in which the leaders reiterated “our commitment to ensure broad participation” at the summit’s high-level session.

“The Conference will be an invaluable opportunity to rethink the current models of development,” the statement added.

Stern’s comments came on the same day when the top U.N. climate official played down any expectations that the Rio+20 summit would produce any binding agreements.

In a briefing hosted by the U.N. Foundation in Washington, UNFCC executive secretary Cristiana Figueres said the meeting “is not a technical negotiation.” where “countries agree on the legal structure that is going to be the guiding or underpinning [for a] collective effort.”

”Rio is about a bigger conversation,” she said. “What kind of society do we really want? What are we headed to?”