WASHINGTON - For a new president, there inevitably comes that moment: the first time he hears a foreign crowd hoarsely chanting his name, or sees thousands of well-wishers surging forward, or realizes youngsters are running pell-mell beside his motorcade, desperate for a glimpse of his face.

For Barack Obama, the moment came in Cape Coast, Ghana - in the teeming streets near a West African castle where traders once shipped human chattel to a life of toil in the New World.

After a week of difficult summitry in Russia and Italy, trying to get balky allies to follow his lead, Obama was treated to an outpouring in Ghana that can only be called rapturous - from Africans overjoyed at the visit of America's first black president to a country south of the Sahara.

And after feeling this kind of love, it must be cruelly hard to go home.

Awaiting Obama in Washington: an ever-more-painful recession and two of the biggest fights of his young presidency - over health care and energy.

As he toured Europe and Africa, a group of conservative Democrats sought major changes to the health care overhaul House leaders are working on - and in so doing, forced a delay. At a news conference in Italy, Obama sought to downplay that, repeating his call for action by the August congressional recess, but it was clear his top agenda item had hit a speed bump.

Meantime, though Obama bragged to the allies about House passage of energy legislation that would impose the first limits on greenhouse gases, the coalition on global warming was fragile, and the measure's fate in the Senate remains uncertain. The House bill aims at an 80 per cent reduction in emissions of greenhouse gases by mid-century by putting a price on each ton of climate-altering pollution.

But the start of Obama's latest foreign trip was a hard diplomatic slog, too.

In Moscow, Obama and Russian President Dmitry Medvedev agreed to negotiate a new nuclear arms accord to replace START I, which expires in December. However, he left Moscow with disputes over missile defence, Russia's neighbour Georgia and Moscow's treatment of dissidents unresolved.

In L'Aquila, Italy, the G-8 Summit ended on a similarly inconclusive note, as developing nations balked at G-8 calls to halve greenhouse gas emissions by mid-century.

Which must have made the Ghanaian effusion all the sweeter.

It began in the capital, Accra, where parliament treated him to a cheering welcome, heralded by a merry trombone-blast fanfare. "I have the blood of Africa within me," Obama declared, before predicting a new African dawn if the continent can throw off its history of coups and corruption.

But the White House had purposely not scheduled any large, outdoor events in the capital, so the reception there was subdued. Aides said Obama wanted the focus on his message, not him. They also wanted no repeat of President Bill Clinton's open-air speech in 1998 - after which he was nearly trampled by a jubilant throng.

In Cape Coast, a 40-minute helicopter ride from Accra, any such qualms were swept away.

In this one-time headquarters of Britain's Gold Coast slave trade, Obama's likeness was everywhere on placards and billboards. Thousands jammed his motorcade route from the muddy soccer field where he landed to Cape Coast Castle - waving, cheering, chanting, the women ululating, children climbing trees and clambering atop boxes for a better view. They wore T-shirts bearing his likeness, and his campaign motto "Yes We Can."

His wife, Michelle, the great-great-granddaughter of slaves, was in the armoured sport utility vehicle beside him. His daughters, Malia, 11, and Sasha, 8, were along for the ride, also marveling at the sight.

As the motorcade pulled up at the castle, drummers kept up an insistent beat, and a PA announcer blared, "Let us welcome His Excellency, President Barack Obama!"

Inside the whitewashed fortress, the first family got a tour of the oven-like brick dungeons where slaves were crammed as they awaited their fate. The Obamas walked through the "Door of No Return" - the gateway through which thousands passed to ships bound for America - and paused in contemplation, arms around each others backs.

Afterward, the president called the castle "a place of profound sadness." He told reporters it put him in mind of Buchenwald, the German concentration camp he saw last month - evidence of "the capacity of human beings for great evil."

Yet he also found it inspiring, and hoped Malia and Sasha would grasp its import. "It is here where the journey of much of the African-American experience began," he said.

Back in Accra, after a quick hotel stop for a change of clothes, Obama took part in a final airport send-off, complete with drumming and twirling dancers in colorful tribal garb.

"Every day with its success, Ghana sends a simple message to the world, that democracy can thrive in Africa," Obama declared. "Great days lie ahead for this nation. The future is on Ghana's side."

Even Ghana's President John Atta Mills, the unsentimental lawyer who took power in January, was ecstatic.

"There is not a single Ghanaian who is not excited by your visit," he enthused. "The good Lord has heard our prayers, and you have come."

Heavy stuff for a young American president just six months on the job.