Barack Obama moved yesterday to establish tighter emissions standards for cars, erasing any doubt about his plans to put the green agenda at the heart of his presidency.

Making his first appearance in the East Room of the White House, Mr Obama said he was instructing the new head of the Environmental Protection Agency to reconsider a Bush administration ruling that blocked a Californian request to impose more restrictive emissions limits on light vehicles.

It seems all but certain that the agency will give California a waiver to allow it to impose standards tougher than those set at federal level. At least 13 other states, including New York and New Jersey, would likely follow suit.

Download the new Independent Premium app Sharing the full story, not just the headlines

The action clearly aimed to send the message that Mr Obama will be embracing environmental activism with an enthusiasm not seen at the top of US government for eight years, perhaps ever. And he cast the message not just in terms of protecting the planet but also of national and economic security.

"It will be the policy of my administration to reverse our dependence on foreign oil while building a new energy economy that will create millions of jobs," he said. Initiatives to make the US energy-independent – an ambitious, if not pie-in-the-sky, goal – form part of the $825bn (£590bn) economic stimulus plan Mr Obama is trying to sell to Congress, against some resistance.

With yesterday's televised ceremony, Mr Obama also sent a message to his allies that the years of America playing coy with international efforts to cap emissions and combat global warming, if not obstructing them, are over.

"We will make it clear to the world that American is ready to lead," he said as his Secretary of State, Hillary Clinton, was preparing to appoint a new special envoy for climate change.

The job will go to Todd Stern, who advised the former president Bill Clinton on global warming and was closely involved in the Kyoto treaty and Buenos Aires climate-change negotiations. "The days of Washington dragging its heels are over. My administration will not deny facts. We will be guided by them," Mr Obama said, a reference to the record of the Bush White House, which queried the link drawn by scientists between climate change and human activity and resisted calls for a global regime of emissions ceilings.

"For the sake of our security, our economy and our planet, we must have the courage and commitment to change," Mr Obama said.

Tilting at Mr Bush has become a hallmark of the Obama presidency. Even before his first week in office is over, he has repudiated his predecessor's policies by moving to close Guantanamo Bay, reinstate curbs on torture, close secret CIA prisons and resume aid to family planning groups abroad that accept abortion. On car emissions, he said Washington had "stood in the way" of California which has long taken the lead in the US in pushing to curb air pollution and emissions. Governor Arnold Schwarzenegger had written to Mr Obama on his swearing-in asking him to free California to move forward with the caps.

Mr Obama also ordered the transport department yesterday to issue by March the regulations that will help the car industry to meet a law passed by Congress last year designed to increase the miles-per-gallon standards on new cars in time for the 2011 model year.

The Bush administration had neglected to work on the specific regulations, without which it would have been difficult to enact the law, which intends to enforce a 40 per cent improvement in mileage performance in cars by 2020.

Regarding California's initiative, the Bush White House took the view that allowing states to set their own emissions standards would create a messy patchwork of regulations across the country, making it harder for the car manufacturers to comply.

Mr Obama's decision was seen by some as creating a further burden for the struggling Detroit car industry. California's proposed restrictions would force car-makers to undertake a complete retooling to cut greenhouse gas emissions by 30 per cent in new cars and light trucks by 2016.

The Ohio senator George Voinovich said: "I am fearful that today's action will begin the process of setting the American auto industry back even further. The federal government should not be piling on an industry already hurting in a time like this."

Environmental lobby groups praised Mr Obama. "By beginning this process and directing [the environmental protection agency] to review the Bush administration's lack of action, President Obama is turning the federal government into a force for positive change instead of a roadblock," the Sierra Club said.

Meanwhile, the Senate last night confirmed Timothy Geithner, the former head of the New York City Federal Reserve branch, to be Mr Obama’s Treasury Secretary in a 60-34 vote. It had been one of Mr Obama’s most troubled nominations: Mr Geithner had been criticised for failing earlier to pay some taxes, which have now been paid.