CAMBRIDGE, Mass. — President Clinton is praising Mayor Bloomberg’s emphasis on environmental issues.

Addressing more than 400 people at the Charles Hotel under the auspices of a Harvard Kennedy School of Government conference, “The Looming Crises: Can We Act in Time?” Mr. Clinton spoke Friday for more than an hour and a half, covering such subjects as nuclear proliferation, health care, and the environment. The former president cited Mr. Bloomberg’s support for a congestion tax as an example of growing world interest in the environment today.

“I’ve never seen such an explosion of interest. The mayor of New York City just announced a big plan. He proposed a congestion tax, which I think most people [would support] to keep us from having to wait in line all day,” Mr. Clinton said.

He contrasted the interest in the environment today to his presidency, when his advocacy of the issue was greeted with yawns, even at a speech to the National Geographic Society.

New York City’s economy could grow if it became an environmental leader, Mr. Clinton said. “Eighty percent of our gas emissions in New York City are from buildings and the electricity associated from powering them. We have 950,000 buildings in New York,” he said. “If we decided to green every roof and replace all the glass and replace all the lighting, it would have a dramatic impact on reducing greenhouse gases, and the number of new businesses and new jobs that would be created in doing that are staggering.”

Mr. Clinton painted a picture of New York City thriving as a leader in green technologies. “If the mayor had the money to say, ‘We are going to green roof every building we can green roof,’ … think about the breathtaking infusion of jobs that would be. Then we could have training to teach people how to do that,” he said.

While Mr. Clinton did not speak in conjunction with his wife’s campaign, such appearances are nonetheless a boon to the New York senator’s presidential ambitions. “It reminds everyone in a very positive way about what the Clinton years were like,” a professor at Harvard’s Kennedy School of Government and former adviser to Mr. Clinton, David Gergen, said. “It’s widely understood that the two of them together are stronger than just her alone.”

In response to a question near the end of his expansive remarks, Mr. Clinton talked for more than 11 minutes about a subject close to his heart, the prospects for peace in the Middle East.

“If our long-term goal is to try to minimize the number of groups like Al Qaeda that want to conduct terrorism both within the Middle East or beyond, they wouldn’t all go away if the Palestinians and the Israelis made a comprehensive agreement, but half of the energy behind this would collapse,” Mr. Clinton said.

“I don’t think there is anything that we can do today on the terror front in a preventive way that is more important. … We’ll never ever really turn the tide on terror until it’s done.”

If Israel and the Palestinian Arabs could ever come to such an agreement, Mr. Clinton said, America would have to “be prepared to give a security guarantee both to Israel and the new state of Palestine,” though he warned of the danger members of the Palestinian Authority would face.

He said he was proud of his role in promoting negotiations between Israel and the Palestinians. “I didn’t consider it a failure,” he said. “I thought we were closer to peace than ever before. At least everybody knows what a peace agreement will look like.”

Mr. Clinton also spoke of the danger of Iran developing a nuclear weapon, saying he was more worried about a terrorist group obtaining an Iranian bomb than the Islamic Republic using it itself. “Maybe some Iranian leader would think, maybe I can nuke Israel … but we can handle that with a phone call,” he said. “If a nuclear bomb ever exploded in the Middle East, even if it wiped out Israel, the main victims eventually would be all the Muslims around it who would be killed in the nuclear fallout.”

Mr. Clinton’s comments about Iran seemed at odds with those of Senator Clinton, who has spoken of having him serve as a kind of ambassador at large if she is elected president.

Addressing the American Israel Public Affairs Committee in February, Mrs. Clinton said: “We cannot, we should not, we must not, permit Iran to build or acquire nuclear weapons. And in dealing with this threat as I have said for a very long time, no option can be taken off the table.”

Mrs. Clinton’s campaign did not respond to calls and e-mails seeking comment yesterday.