Britain's Queen Elizabeth II arrived in Trinidad and Tobago on Thursday to a wave of enthusiasm but also concern as some world leaders wonder if they can reach an agreement on climate change ahead of an upcoming international summit, and some in the Caribbean question whether they should remain tethered to the British monarch.

The queen's rare visit to the region -- her third to oil-rich Trinidad since 1966 -- comes as the Commonwealth Heads of Government hold meetings in Port of Spain through Sunday. Climate change is expected to dominate discussions among 50 of the 53 self-governing members of the former British empire.

The summit will also feature French President Nicolas Sarkozy, Danish Prime Minister Lars Lokke Rasmussen and U.N. Secretary General Ban Ki-moon. Although none heads a Commonwealth nation, the four have been invited to help forge an agreement on climate change before the U.N.-sponsored Climate Change Summit in Copenhagen, Denmark, next month. That gathering is expected to attract at least 65 world leaders, including President Barack Obama.

``Already, this is turning out to be one of the largest major gatherings of political leaders and heads of governments before next month's summit in Copenhagen,'' said Ben Malor, a spokesman for Ban.

``This is an opportunity where the Secretary General is going to drive up the momentum toward Copenhagen, asking and urging the leaders to make sure success is achieved in Copenhagen because failure would be too costly.''

Malor said Ban will have bilateral meetings with several of the 39 Commonwealth leaders who will be in Trinidad. He will also participate in an executive session on climate change on Friday, as well as discussions on small island developing states, which are being heavily impacted by rising sea levels. There also will be a separate meeting with Australia's prime minister and the least developed countries of the world, focusing on economies and livelihoods.

Earlier this week, the Australian government proposed a pledge of $46 million to assist Grenada and other Caribbean countries in areas including climate-change mitigation, agriculture and small-business development. Australia is seeking to develop stronger ties with the Caribbean.

A RAISED PROFILE

This is the second time this year that Trinidad and Tobago, a natural gas- and petroleum-rich eastern Caribbean nation, is at the center of a diplomatic gathering of huge significance.

In April, the country hosted Latin American leaders along with Obama and U.S. Secretary of State Hillary Clinton during the Fifth Summit of the Americas.

``We have the opportunity to positively influence its outcome,'' Trinidad and Tobago Prime Minister Patrick Manning said about his tiny twin-island nation's big role in the climate-change talks. ``Trinidad and Tobago is doing its utmost to advance the process that could result in a global agreement on this crucial matter affecting all of humanity.''

Just as in April, security measures will be tight throughout Trinidad, where traffic around Port of Spain will be rerouted and hundreds of Caribbean troops will keep a close watch over leaders, including India's Prime Minister Manmohan Singh, fresh from an official visit to the White House this week.

One Commonwealth leader who won't be traveling to Port of Spain: the president of the small West African country of Gambia, who in September threatened to kill human-rights workers.