LONDON — Setting the stage for a G-8 summit starting Thursday in France, President Barack Obama spoke Wednesday from one heart of "Old Europe" to assert that the U.S.-European alliance will lead the 21st century even as new powers such as China, India and Brazil emerge.

Flatly rejecting the notion that Western civilization has peaked, Obama instead insisted that the free people and free markets that forged a new order from the ashes of World War II remain essential to global leadership in economics, politics and security arrangements, especially as turmoil spreads across the Middle East and North Africa.

"Perhaps, the argument goes, these nations (China, India, Brazil) represent the future, and the time for our leadership has passed," Obama said. "That argument is wrong. The time for our leadership is now."

He spoke to both houses of Parliament at Westminster Hall, a cavernous, church-like structure that is the oldest part of Parliament. Built between 1097 and 1099 by the son of William the Conqueror, it was the site of royal feasts and later home to the nation's judiciary, where it hosted such historic trials as those of Sir Thomas More in 1535 and King Charles I in 1649.

Obama was the first U.S. president ever to speak there; others including Ronald Reagan and Bill Clinton addressed Parliament in the Royal Gallery.

Paying homage to history, Obama saluted the English for developing the rule of law and the rights of citizens, values that he said inspired the United States and set a model for the world. With allied powers, he said, they built the modern global order.

"It was the United States and the United Kingdom and our democratic allies that shaped a world in which new nations could emerge and individuals could thrive," he said.

It was England and America that developed the free-market capitalism that now lifts China, India and Brazil to prosperity, he noted. And it is the U.S.-European alliance that stands up most for human rights against government oppression, he said, in an implicit slap at China.

"And even as more nations take on the responsibilities of global leadership, our alliance will remain indispensable to the goal of a century that is more peaceful, more prosperous and more just," he said. "At a time when threats and challenges require nations to work in concert with one another, we remain the greatest catalysts for global action."

His statement of faith in the U.S.-Europe alliance came as he looks to it to help the world pivot from the troubled last decade, as wars in Afghanistan and Iraq wind down, the world recovers from a wrenching recession, and the death of Osama bin Laden signals a turning point against terrorism.

Topping the agenda is helping to usher in a new era of democracy across the Middle East and North Africa. That will dominate talks as he meets Thursday and Friday in the old seaside resort of Deauville, France, with leaders at a summit of the world's eight leading industrialized democracies — the United States, the United Kingdom, France, Germany, Italy, Canada, Japan and Russia — the Group of Eight, or G-8.

The G-8 allies also will meet with leaders from Egypt and Tunisia who recently overthrew their autocratic governments. The Group of Eight is expected to promise them aid to help them transition to democracies and develop their economies, as Obama called for last week in a major address on change in the Middle East.

Heading into the G-8 summit, some allies signaled that they're eager to increase air strikes in Libya to force dictator Moammar Gadhafi to give up power more than 60 days after the NATO alliance moved to stop him from attacking his fellow citizens.

French Defense Minister Gerard Longuet said the French and British were preparing to deploy attack helicopters, capable of more precise strikes.

British Prime Minister David Cameron, appearing with Obama in London, sidestepped a question about the helicopters, but he did say that he wants to bring more force to bear on Gadhafi.

"The president and I agree that we should be turning up the heat in Libya ... we should be turning up that pressure," Cameron said.

While the United Nations resolution authorizing NATO strikes in Libya limited their goal to protecting citizens and did not authorize driving Gadhafi from power, Cameron said that is ultimately the only way to protect the Libyans.

Obama appeared happy to let the Europeans continue to take the lead on Libyan air strikes, albeit with occasional hits from U.S. predator drones. He also signaled that more effort is needed by anti-Gadhafi rebels, who met this week with a U.S. official.

"Once you rule out ground forces, then there are going to be some inherent limitations to our air strike operations," Obama said. "It means that the opposition on the ground in Libya is going to have to carry out its responsibilities. And we're going to have to do effective coordination, and we are doing that, with the opposition on the ground."

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