The latest survey of Americans shows that more than half are now opposed to abortion, marking a significant shift in opinion in recent years.
The Gallup poll, when first conducted in 1995, revealed that abortion was supported by 56 per cent of the population, with 33 per cent opposed.
In this year’s poll, however, 51 per cent of Americans called themselves pro-life, against 42 per cent who say they are pro-choice.
Other Gallup figures also show that over half the population consider the views of political candidates to be an important factor in who they vote for.
Most opposition to abortion is found among America’s under-30s.
Abortion was made legal in America in 1973 through judicial activism when the Supreme Court ruled on the case of Roe v Wade.
However, the plaintiff referred to as Roe, Norma McCorvey, now opposes abortion. She was among more than 300 protestors who gathered outside Notre Dame University yesterday as President Barack Obama prepared to give a speech.
Mr Obama, who was receiving an honorary degree from the Roman Catholic university, was heckled by pro-life protesters.
He told the audience that he wanted to see fewer abortions, and said the pro-life and pro-abortion positions were ultimately irreconcilable.
“Each side will continue to make its case to the public with passion and conviction”, he said. “But surely we can do so without reducing those with differing views to caricature.”
When he became president Mr Obama pledged to oppose any constitutional amendment to protect the lives of unborn children, and said he would actively defend the Roe v Wade ruling.
He committed himself to ending a ban on federal funding for international pro-abortion groups, which he has already carried out. He has also lifted a ban on federal funding for stem cell research using human embryos.
Americans are currently waiting to see who Mr Obama will appoint as the next Supreme Court judge after the retirement of Justice David Souter. Pro-life groups hope that the Roe v Wade decision will eventually be overturned.