Mayor Bloomberg this week is going global with his environmental platform, seizing on a politically hot issue just as speculation is intensifying about whether he is considering running for president.

The mayor will be sharing the spotlight with President Clinton — a point not lost on those watching Mr. Bloomberg to see if he’s going to make a run for Mr. Clinton’s old job at the White House. The two will be delivering the keynote speeches and playing host to the so-called C40 Large Cities Climate Summit, a three-day gathering expected to draw more than 250 high-power business leaders and mayors from cities including London, Singapore, Tokyo, Rio de Janeiro, Sydney, and dozens of others from around America and the globe.

The event, which starts today, comes days after Mr. Bloomberg outlined his energy-policy positions in Houston. He called on the federal government to increase fuel standards for automobiles, to create incentives for purchasing hybrid cars, and to build up wind farms and nuclear power plants. The event also comes less than a week after the mayor relaunched his dormant campaign Web site, which now has all of the hallmark signs of a revived political campaign.

Mr. Bloomberg’s emergence as an international spokesman on the environment is being pegged to PlaNYC, his 127-part proposal to reduce the city’s greenhouse gas emissions and make New York an environmental leader.

“He’s put forward a plan for New York City that is one of the most practical and ambitious environmental plans of any world city,” the regional director of Environmental Defense, Andrew Darrell, said. “I think it’s for that reason that he has the credibility to speak to the issue on a world stage.”

At the heart of Mr. Bloomberg’s PlaNYC is a proposal to charge cars and trucks traveling into the center of Manhattan during peak hours. The mayor will be in Albany today meeting with lawmakers to sell that measure, the most controversial of the lot.

The combination of Mr. Bloomberg’s Houston speech, his trip to Albany, and his role at the summit have been so closely timed that they have taken on the feel of a carefully orchestrated cross-marketed advertising blitz.

Indeed, the Environmental Defense and the Partnership for New York City, two of the organizations backing the Bloomberg plan, today are launching a 30-second television advertisement supporting the proposal and suggesting catastrophic consequences if action is not taken.

The president of the partnership, Kathryn Wylde, whose group is also one of the organizers of the climate summit, said she does not think Mr. Bloomberg’s high-profile role at the summit has anything to do with politics. She said the mayor is simply using the bully pulpit that results from his unique position as the founder of a worldwide financial news organization and the leader of New York City to push for an important policy goal.

“He’s somebody that’s totally comfortable on the international stage,” she said. “And, the issues that are most important to him are also global concerns. It’s natural that he is maximizing the platform that he has as mayor.”

The summit, the second annual C40 conference, will draw CEOs and executives from mega-companies including Citigroup, Time Warner, Siemens, and Alcoa, a major producer of aluminum. The CEO of Time Warner, Richard Parsons, who has been named as a possible 2009 Republican candidate for mayor, will host a dinner for the international delegates. Mr. Bloomberg will be hosting a dinner tonight at Gracie Mansion.

The event — which is expected to draw hundreds of national and international reporters — will not be the first time Messrs. Clinton and Bloomberg have shared the spotlight. The two delivered keynote speeches on back-to-back days at a philanthropy conference at the Clinton Presidential Library in Arkansas in November. A number of others mayors, including London’s Ken Livingstone, who has already implemented a congestion pricing charge in his city, will also be making presentations.

A political consultant, Joseph Mercurio, noted that Mr. Bloomberg has gone from an unknown on the environmental stage to one of the key players.

“Here’s a guy who had not been at all identified with environmental issues,” Mr. Mercurio said. “All of a sudden now he’s a major player on the stage.

“Because of his wealth and his position as mayor of New York he could influence in the policy debate in a major way,” Mr. Mercurio said. “The question is will he influence public policy as a philanthropist and a major spokesperson on important issues or if he’s going to try and do it from the position of the Oval Office.”