In an interview with Time magazine, Geldof said he recently defended Bush in France on that score.
"They refuse to accept, because of their political ideology, that he has actually done more than any American president for Africa," said Geldof. "But it's empirically so."
U2 singer Bono, who also participated in the interview, said Bush could still show more commitment to Africa.
"He feels he's already doubled and tripled aid to Africa, which he has," said Bono. "But he started from far too low a place. He can stand there and say he paid at the office already. He shouldn't, because he'll be left out of the history books."
Bono acknowledged that Bush is limited by the expense of war and growing U.S. debt.
"But I have a hunch that he will step forward with something," said the Irish rocker.
Geldof, Bono and screenwriter Richard Curtis are the main organizers behind the upcoming Live 8, a series of free concerts scheduled for July 2. A show in London will feature Pink Floyd reunion on a bill with U2, Coldplay, Madonna and Paul McCartney.
Live 8 is intended to build public support for debt forgiveness and other aid for Africa by the world's major economic powers.