A coalition of campus and environmental activists plans a series of rallies across the country on Saturday to call for federal officials to control global warming.

Three Democratic presidential candidates — Christopher J. Dodd, John Edwards, and Dennis J. Kucinich — have said they would attend one of the events, said the organizers of the coalition, Step It Up. At least one rally will be held on a campus, at Arizona State University at Tempe.

In a news release, the organizers said the events were meant to “show the contrast between the intense concern of ordinary Americans and the leadership vacuum in Washington.” In addition, college students are planning to hold a rally on Monday on Capitol Hill about climate change.

So far, the Democratic candidates for president have voiced largely similar ideas about controlling the greenhouse gases that cause global warming, while the Republicans are more split. The Democratic leaders of Congress are expected to introduce legislation this year or next to control emissions.