(Updates throughout with auto fuel economy, Clinton, edits)
By Deborah Zabarenko, Environment Correspondent
WASHINGTON, April 22 (Reuters) - Google went green and so did dozens of comic strips while President George W. Bush planted a tree on Tuesday to mark Earth Day, an environmental event that has become increasingly political and corporate.
Thirty-eight years after Earth Day began as a series of grass-roots "teach-ins" about environmental conservation and pollution, April 22 has become an occasion to focus attention on human-generated climate change and the policies around it -- a topic not on the public mind in 1970.
The method for getting the message across has certainly evolved. Google.com's online search site featured a lush logo with letters made of moss-covered boulders, a tree sprouting from the "L" and a waterfall flowing beneath it. Clicking on the image led to a list of Earth Day-related sites.
The comics pages in many U.S. newspapers featured strips with environmental themes. "Zippy The Pinhead" was typical: the short-sighted residents of Dingburg save the Earth by packing dirt into suitcases and keeping them in a storage locker.
Bush was in New Orleans for the so-called "Three Amigos" summit with leaders from Canada and Mexico, where the U.S. president planted an oak tree in Lafayette Square -- a symbolic replanting of the some 250,000 trees stripped away from the city by 2005 hurricanes Katrina and Rita.
PLAN TO RAISE FUEL EFFICIENCY
The Bush administration, which has weathered criticism for its stand on environmental issues, offered a plan on Tuesday to boost fuel economy for cars and trucks to cut U.S. dependence on foreign oil and curb greenhouse gas emissions.
The plan would require the U.S. and international fleet to average 32 miles per gallon (13.6 km per litre) by 2015. The energy bill Bush signed in December requires that autos average 35 miles per gallon (14.9 km per litre) by 2020, a 40 percent increase over the current standard.
On the presidential campaign trail, Democrats Sen. Barack Obama and Sen Hillary Clinton and Republican Sen. John McCain offered statements urging a focused U.S. environmental and energy policy.
"Our leaders in Washington have to put what's right for our planet ahead of what's good for their friends in the energy industry," Obama, an Illinois senator, said in a statement on the day of the presidential primary in Pennsylvania, where he is in a tight race with Clinton of New York.
"I will end the Bush administration's assault on environmental protections and standards," Clinton said. "...It will be a new day."
"We must have the courage to realistically confront the specter of climate change," McCain said in his statement. "This is one of the greatest challenges confronting the next president."
LAWS AND LIGHTBULBS
U.S. House Speaker Nancy Pelosi, joined by fellow members of Congress and religious leaders, marked the day by helping plant an elm tree outside the U.S. Capitol.
"We can make a difference," said Pelosi, a California Democrat who has taken a lead in addressing global warming. "It is a national security issue, it is an economic issue, it is an environmental and therefore a health issue, and it is a moral issue."
In a separate move, Democratic Reps. Ed Markey of Massachusetts, Henry Waxman of California and Jay Inslee of Washington state said any effective climate-change law must reduce emissions to avoid dangerous global warming, shift the United States to clean energy, minimize the law's economic impacts and aid communities and ecosystems at risk from global warming.
The U.S. Environmental Protection Agency, under fire from critics who contend the agency has failed to curb the greenhouse gas emissions from fossil-fueled vehicles that spur climate change, launched a national campaign aimed at cutting emissions in U.S. homes.
Participants in the program include Amazon.com, Best Buy, Hewlett-Packard, Lowe's, Menards, Sears, and Subway, the agency said in a statement.
The Washington Post, noting the change in the celebration from previous years, wrote a tongue-in-cheek essay declaring Earth Day dead: "What killed it? A long but admirable struggle with celebrity piety and corporate baloney, mainly." (Editing by Philip Barbara)
(For more Reuters information on the environment, see blogs.reuters.com/environment/ )