Bush inched towards Blair's position on writing off impoverished nations' debt and praised his close ally on Tuesday for pressing Africa's cause.
He offered little to encourage Blair's hopes of mounting a concerted international fight against global warming.
The prime minister travels next week to Moscow, Berlin and Paris to continue his whirlwind campaign to bring leaders of the G8 group of industrialised nations together on the two issues he has made the centrepiece of Britain's year-long chairmanship of the club.
"I'm grateful for your vision, and I'm grateful for your leadership on this important subject," aid to Africa, Bush told Blair at a White House news conference. "We're making historic progress in helping the poorest countries in Africa gain a fresh start and to build a future of greater opportunity and prosperity."
Elimination of debt
The leaders said they were working together on a plan to eliminate poor countries' debt, and Blair said he was hopeful they'd have a deal in time for the July summit at the Scottish resort Gleneagles.
Bush appeared to move towards the British position on a detail that is important to the prime minister, that the money used to cancel debts must not come out of future aid.
"The brutal truth is, without America in a process of dialogue and action in the international community, we are not going to make progress on it"
British prime minister
The president said the proposal in the works, "by providing additional resources, will preserve the financial integrity of the World Bank and the African Development Bank," which distribute much of the aid.
Bush also promised $674 million for famine relief in Africa, a commitment Blair described earlier as only a small step towards the $25 billion he wants rich countries to pledge to add to aid annually in order to double it within three to five years.
The American promises so far may fall short of the huge effort Blair is calling for to help Africa get on its feet with a mix of trade, aid and debt relief.
"We're trying to create a framework in which we deal not just with one of the issues to do with Africa, but all of them together," he said.
"In a situation where literally thousands of children die from preventable diseases every day, it's our duty to act, and we will."
Speaking to the House of Commons back home on Wednesday, Blair said: "We have begun a discussion which I hope will end up with a plan for action at the G8 summit."
"The brutal truth is, without America in a process of dialogue and action in the international community, we are not going to make progress on it," Blair told lawmakers, vowing to continue the dialogue with the White House.
European Union nations agreed recently to double aid to Africa, as Blair has urged.
Good governance stressed
Bush said the United States has tripled its aid to the continent, and the traditional measure of a country's aid effort - percentage of gross national product, which shows the
United States among the most miserly of the rich nations - was not the right way to measure America's commitment.
Blair won no substantive US
concessions on global warming
Blair echoed much of the language Bush has used in pushing his Millennium Challenge Account programme for Africa, which ties aid to good governance.
"It is a two-way commitment," Blair said. "We require the African leadership also to be prepared to make the commitment on governance, against corruption, in favour of democracy, in favour of the rule of law... What we're not going to do is waste our countries' money."
Blair succeeded in making his G8 wish list the main topic of his meeting with Bush, which also covered Iraq, Iran, the Middle East peace process and Afghanistan.
The two dined together after speaking to the media.
Blair acknowledged he had a lot of work ahead if the Gleneagles summit is to end with an Africa deal.
Agreement with America on global warming seems further away.
Blair won no substantive concessions on the issue, which highlights the political differences between the conservative Republican president and his centrist Labour Party ally.