An initiative led by former President Clinton (search) to tackle poverty, climate change and other worldwide issues is launching with a gathering of political leaders and activists who are promising to pitch in -- and must put those pledges in writing.

Participants who fall short can't come back next year, said Jay Carson, spokesman for the Clinton Global Initiative (search).

Among the 800 expected at a Manhattan hotel for the three-day event beginning Thursday are British Prime Minister Tony Blair (search), Secretary of State Condoleezza Rice, U.N. Secretary General Kofi Annan, and Clinton himself.

"This conference is not about talk, it's about action," Carson said. Clinton has been "very clear that if people aren't here to make a difference, then they're at the wrong conference."

Some commitments have already been lined up, including establishment of a $100 million foundation to fight poverty, and others will come out at the meeting, Carson said.

Clinton's wife, Sen. Hillary Rodham Clinton (search), is speaking on a panel. Other notables include financier George Soros and media chiefs Rupert Murdoch and Richard Parsons. Many participants are already in the city for a summit marking the 60th anniversary of the United Nations.

Mingling with them will be representatives from non-governmental organizations and the business community. Among the topics: clean energy and how to finance it, battling poverty, and Islam and the West.

Admission is an expensive ticket, with some attendees paying $15,000 to attend -- the fee was waived for others -- but the key is the promise of action, Carson said.

"President Clinton has attended a number of other conferences and feels that they play a critical role in terms of getting people together and discussing important issues," Carson said. But "he feels like we've reached the time where it's not enough just to talk about the issues."

The initiative's staff will track whether contracts are fulfilled, Carson said.