The increase includes initiatives to battle malaria, provide legal protection for women and education to girls. The aid plans impressed some advocacy groups, even though they said most of the doubling would come from already-pledged money.
"Across Africa, people who were preparing to die are now preparing to live, and America is playing a role in so many of those miracles," Bush said in a wide-ranging speech.
Bush is preparing to attend a meeting next week in Scotland of major industrial countries and Russia. The summit host, British Prime Minister Tony Blair, has made Africa a top item for discussion.
Bush's initiatives go along with $674 million in emergency famine relief announced this month and an agreement on Africa debt relief.
They help the president blunt criticism of his rejection of Blair's proposal for summit countries to increase aid to Africa to 0.7% of their gross national product.
Bush says agreeing to Blair's plan is not necessary because aid has tripled during his presidency, though the US gives far less as a proportion of national income than most other industrialised nations.
"Across Africa, people who were preparing to die are now preparing to live, and America is playing a role in so many of those miracles"
US President George Bush
National security adviser Stephen Hadley said Bush's new proposal would raise US assistance to Africa to $8.6 billion in 2010, from $4.3 billion in 2004.
Those figures include aid that is channelled through organisations such as the World Bank. The Reverend David Beckmann, president of Bread for the World, said Bush's promise would be achieved mainly by offering debt relief and fulfilling past commitments.
But Beckmann, whose Washington-based organisation lobbies to end hunger, said that level of aid would make "the US a serious partner in the global effort to reduce poverty in Africa".
That, he said, "should be a plus for how people around the world view the United States".
Chad Dobson, policy director for the charity Oxfam America, hoped the announcement would mark the beginning of a much larger US commitment. He praised it as creating "the momentum that is needed" going into the Scotland meeting.
But critics dispute Bush's claim that assistance has tripled on his watch. They say his administration undercounts what was spent in the Clinton years and overcounts that spent during his own presidency.
A Brookings Institution study this week said that in 2000, the last year of the Clinton administration, total spending on Africa aid was $2.3 billion.
The total for 2004, the last completed year of the Bush administration, was $3.4 billion or just over a 50% increase when aid channelled through multilateral groups is excluded. Much of the increase was in emergency food aid.
In his speech, Bush again termed the violence in Sudan's Darfur region, where civilians are being killed, a "genocide".
He also urged South Africa and other African nations to step up the pressure on Zimbabwe's President Robert Mugabe about human rights abuses in his country.
"Next door to you is a person who is destroying a country because of bad policy and it's not right," Bush said in an interview with foreign reporters to preview the Scotland meeting. "The nations in the neighbourhood must be strong."
Bush also called on Sudan to stop
the 'genocide' in Darfur
In his speech, the president proposed increasing spending to $1.2 billion to cut the death rate from malaria in 15 African nations in half by 2010.
One million people die from the mosquito-borne disease every year around the world, and it is one of the top killers in Africa. Bush requested $58 million to fight malaria for 2006, down from his $61 million request for 2005.
The president also proposed spending $400 million over four years to train 500,000 teachers; provide scholarships to 300,000 young people - most of them girls; build schools; and buy textbooks in 16 countries.
He said he would ask Congress for $55 million over three years to improve legal protections for African women against violence and sexual abuse.