Fifty mayors from around the world signed an environmental accord in San Francisco Sunday, which the United Nations had designated World Environment Day. The agreement marks the most far-reaching effort to date by city leaders to tackle environmental problems.

The signatories included mayors or city officials from Chicago, Capetown, Istanbul and Jakarta. Fifty cities approved the agreement, out of 70 expected at the conference.

This is the first time the annual meeting of the U.N. Environment Program was held in the United States. Also for the first time, the focus was on cities and not nations.

The 21 so-called actions outlined in the document are ambitious, covering areas such as transportation, health, energy and water. One provision calls for a 25-percent reduction in the emission of greenhouse gases, including carbon dioxide, by 2030; another for zero waste in landfills and incinerators by 2040.

San Francisco mayor Gavin Newsom notes the agreement is not binding, but cities are asked to implement the provisions step by step over the years.

"Frankly, these are just goals, which are nothing more than dreams with deadlines. The challenge is to take these goals, these ideals, and manifest them," Mr. Newsom says.

The mayors also discussed way to achieve their goals. Winnie Berndtson, mayor for the environment for Copenhagen, Denmark, says her city must deal with air and noise pollution.

"And I think some of the solutions might be given to us by other cities all over the world, and not only European, but also the cities in the United States, for the example, the solar cities you have here are doing excellently," Ms. Berndtson says.

She says cities in developing nations such as India and Sri Lanka are often ahead of industrial countries in recycling.

Denis Hayes was one of the founders of Earth Day, a citizen-sponsored celebration of the environment, which is now observed in 182 countries. He says this meeting is important because municipal governments are joining the environmental discussion. And he says change occurs in local communities.

"You can make any kind of declaration you want as a president or a congress and if it doesn't get implemented, in America say in Cincinnati and Chicago and Miami, nothing is really going to change," Mr. Hayes says.

The mayors shared their concerns in five days of discussions. The mayor of Surabaya, Indonesia, wants more accurate measures of air quality to better inform his people about daily conditions. The mayor of Stockholm spoke about plans to modernize a water treatment plant to reduce nitrogen emissions. A city official from Kiev, Ukraine, hopes to move industrial plants outside his city.

John Ssebaana Kizito, the mayor of Kampala, Uganda, said the meeting taught him solidarity.

"This session in San Francisco has taught me that we must work together to save our earth," he says.

The conference was billed as non-political, but politics was always in the background. Most US cities involved in the conference have endorsed the Kyoto Protocol, including Berkeley, San Francisco and Seattle. The international climate-change agreement imposes strict limits on emissions of greenhouse gases by industrial countries. The Bush administration opposes the treaty, questioning its effectiveness and saying it is harmful to US business.

Officials from some cities declined to sign the document until it is ratified by their municipal government. Five mayors from China cancelled their involvement after learning two mayors from Taiwan would participate.