WASHINGTON -- Before Earth Day became what it is -- an international ritual halfway between a street party and a guilt trip -- it was a bunch of 20-somethings working in an office over a diner.

It was 1970. They worked 15-hour days. They stuffed a lot of envelopes.

And, at first, they didn't like the name.

"Who in the hell do they think we are, the Grange?" Stephen Cotton recalled about reading the name an advertising agency had proposed for their national protest. Earth Day sounded like an event for farmers. "But it grew on us."

Earth Day turns 40 on Thursday, making its founders 60-somethings. To this group of about 20, both the day and the country look very different now.

In those four decades, the angrier, more ambitious environmental movement that sprang out of Earth Day made vast changes in Washington. New federal laws took on dirty air and poisoned water -- and won.

But today, American environmentalism is struggling in a new kind of fight.

The problems are more slippery: pollutants like greenhouse-gas emissions, which don't stink or sting the eyes. And current activists, by their own admission, rarely muster the kind of collar-grabbing immediacy that the first Earth Day gave to environmental causes.

"I don't think we've come up with a good way in the conservation movement of making it real for people," said Arturo Sandoval, who was 22 when he organized activities across the West on the first Earth Day. "Global warming, to most people, is an abstract issue."

Earth Day's 40th anniversary will be celebrated across the globe Thursday: There will be children studying pollution in Baltimore Harbor, a coral-reef cleanup in the Virgin Islands, a concert in Rome. And on Sunday, a climate-focused rally on the National Mall will include performances by Sting, John Legend and the Roots.

The day's beginnings were much humbler, but not that far away. The first Earth Day was organized from an office that smelled like hamburger grease and teemed with flies.

"Every so often, someone would go berserk and dash from room to room" swinging a fly swatter at the swarms drawn by the oily fumes rising from the diner downstairs, said Cotton, then 23, who was the press director for the group. "Since we were budding ecologists, we had an unspoken rule against using bug spray."

He and the other young people were working on an idea from then-Sen. Gaylord Nelson, D-Wisc., who died in 2005. In August 1969, Nelson had visited a huge oil spill off Santa Barbara, Calif. He wondered: Why not hold a "teach-in" -- like the campus discussions that focused on the Vietnam War -- on the environment?

Nelson hired Denis Hayes, 25, a graduate student at Harvard and a former student-body president at Stanford. The rest came from a variety of other liberal causes: a veteran of Robert F. Kennedy's presidential campaign, an organizer of antiwar protests in Mississippi, an anti-hunger activist.

At the time, the Potomac River was choked with pollution-fueled algae blooms. Cleveland's Cuyahoga River had recently caught fire. Smog was so bad that, in 1966, a vast cloud of it was blamed for killing more than 150 people in New York City. And even the bald eagle's population had fallen below 1,000 nesting pairs in the continental United States, ravaged by the pesticide DDT.

The group mailed out suggested Earth Day activities, called college campuses to set up events, talked to dozens of newspaper and TV reporters.

It worked: On Earth Day itself, there was a "human jam" that filled New York City's Fifth Avenue, a rally near the Washington Monument, a march against a foul-smelling sewage plant in Albuquerque, N.M. There were events at college campuses and in classrooms around the country: By one estimate, one in 10 Americans participated.

In the four years afterward, the Environmental Protection Agency was founded and Congress passed a series of landmark laws. The Clean Air Act amendments of 1970 set new limits on pollutants. The Endangered Species Act of 1973 provided new protections for vulnerable animals. And the Safe Drinking Water Act of 1974 set new restrictions on what could come out of taps.

Today, EPA estimates that the Clean Air Act -- amended in 1990 to crack down on acid rain -- has prevented more than 220,000 premature deaths from air pollution. Other legislation led to pollution cuts that have made both the Cuyahoga and the Potomac run cleaner.

And, with DDT banned, there are now more than 9,700 nesting pairs of bald eagles in the Lower 48.

"We won the argument that the environment needs to be protected," said Michael Brune, the modern-day executive director of the Sierra Club. "The conversation is now about at what pace do we need to reform, what are the most effective policy solutions we need to put in place, what the costs are going to be."

The group of organizers disbanded after that first Earth Day and went on to careers in law firms, foundations, environmental groups, state government. But since then, they and other observers have seen the American environmental movement struggle to rebuild its momentum. With rare exceptions, like in the 2006 defeat of then-House Resources Committee Chairman Richard Pombo, R-Calif., the environment rarely serves as the defining issue in national campaigns.

Public opinion polls show that, while Americans care about the environment, they generally rank it behind other priorities like jobs, terrorism and health care. And, on climate change -- the environmental movement's defining issue now -- polls show Americans seeming less concerned, not more, than in previous years.

"I don't think the environmental movement is deep enough, broad enough, to have the impact we want," said Bill Meadows, president of the Wilderness Society, who, like many of today's most prominent environmental leaders, took part in Earth Day events in 1970. "We're a strong interest group, but we have yet to have the kind of political clout you really need in today's political world."