PORT OF SPAIN (Reuters) - Commonwealth states representing a third of the world's people said on Sunday momentum was growing towards a global climate deal, but nagging doubts remained over funding levels and degrees of commitment.

Seeking to successfully tip the outcome of U.N. climate talks on December 7-18 in Copenhagen, the group of more than 50 nations from across the world made the climate change issue the centerpiece of a three-day summit in Trinidad and Tobago.

They declared firm support for an "operationally binding" deal to be achieved in Copenhagen that would cover tougher greenhouse gas emissions targets, climate adaptation financing for poorer nations and transfer of clean-energy technology.

The Commonwealth group, which welcomed Rwanda as its 54th member, called for a full legally binding climate treaty to be adopted "no later than 2010" and insisted fast funding be made available to poor states to counter the global warming threat.

Commonwealth leaders hailed the consensus achieved in their Port of Spain Climate Change Declaration as improving the odds for a comprehensive agreement in Copenhagen and as proof that their geographically diverse group was a viable institution.

"There is heavy traffic on the road to Copenhagen. The good news is that it is converging and hopefully moving purposefully into a single lane," Commonwealth Secretary-General Kamalesh Sharma said in comments closing the Port of Spain summit.

U.N. Secretary-General Ban Ki-moon and the presidents of Denmark and France, had participated in the Commonwealth summit, adding weight to the group's climate deliberations.

"I have no doubt it will make an impact on Copenhagen," South African President Jacob Zuma told reporters.