Federal Opposition Leader Tony Abbott says he can guarantee that his religious views will not impact on policies about women.

The Liberal leader has also backtracked from his previous views on homosexuals and saying the numbers of abortions each year is a "legacy of unutterable shame".

He has told Nine Network's 60 minutes program that he did not say what he meant to and distanced himself from controversial comments he had previously made.

"I didn't express it as well as I could have or should have," Mr Abbott said.

"And I absolutely accept that for any woman facing an unexpected pregnancy, the choices are tough."

"I've certainly said some things which I wouldn't say now. I said some things which I believed then which I don't believe now. Because like everyone who's had a long time in public life - in particular - I've changed and I'd like to think that I've grown."

The devout Catholic says his faith does not dictate his political positions or policies.

"Faith is important to me. It's important to millions of Australians. It helps to shape who I am. It helps to shape my values," he said.

"But it must never, never dictate my politics. Judge me by what the considered view today is, not by throwaway lines and off-hand comments 35 years ago."

Mr Abbott, who as student politician at Sydney University opposed gay rights, also said he no longer has the strong views on homosexuality he used to.

He says was "reasonably unfazed" when his sister, Christine Forster, told him she was a lesbian.

"It came as a bit of a shock when someone who is close to you, who you've always thought of in a particular light, tells you that they're now to be seen in a different light but nevertheless I think I was probably reasonably unfazed by it," he said.

In the interview Mr Abbott reaffirmed his opposition to gay marriage.