Opposition Leader Tony Abbott has been heckled during a speech apologising to the victims of forced adoption practices.

OPPOSITION Leader Tony Abbott has been heckled during a speech apologising to the victims of forced adoption practices.

A number of women in the audience began yelling at Mr Abbott when he used the words "birth parents".

He said: "We honour the birth parents, including fathers, who have always loved their children."

Mr Abbott also acknowledged the efforts of adoptive parents, as those in the audience continued to shout.

"I hear what you are saying ... I honour the parents, who have always loved their children," he said.

"The last thing I would wish to do is cause pain to people who have suffered too much pain already.

"I am happy to retract it."

In some quarters, the term "birth parent" is deemed insensitive to women who relinquished their children under difficult circumstances.

Mr Abbott spoke after Prime Minister Julia Gillard made the long awaited national apology at a special ceremony in Canberra attended by hundreds of people, including mothers betrayed by a system that decided their children were better off elsewhere.

"We apologise," she said.

"We acknowledge your loss and grief."

From the 1950s to the 1970s an estimated 150,000 unwed Australian mothers had their babies forcibly adopted under a practice sanctioned by governments, churches, hospitals, charities and bureaucrats.

Some women were tricked into signing adoption papers, drugged and physically shackled to hospital beds.

Ms Gillard was speaking ahead of parallel motions being moved in the House of Representatives and the Senate later on Thursday to formalise the apology.

It will say that the parliament, on behalf of the Australian people, takes responsibility and apologises for the policies and practices that forced the separation of mothers from their babies.

"This apology is extended in good faith and deep humility," Ms Gillard said.

"It will be a profound act of moral insight by a nation searching its conscience."

Ms Gillard said it took courage to say sorry.

"What we see in that mirror is deeply shameful and distressing," she said.

"A story of suffering and unbearable loss."

The prime minister spoke of young and vulnerable women who lost their children under pressure and sometimes the influence of drugs.

"Most common of all was the bullying arrogance of a society that presumed to know what was best," she said.

"For decades, young mothers grew old haunted by loss."

Ms Gillard also spoke of the children who were adopted, some of whom suffered sexual abuse at the hands of their adoptive parents or in state institutions.

"Many others identified the paralysing effect of self-doubt and a fear of abandonment," she said.

But Australia could not forget the fathers, who were often ignored at the time of the births and whose names were not included on birth certificates.

"No collection of words alone can undo all this damage," Ms Gillard said.

"But by saying sorry we can correct the historical record.

"We can declare that these mothers did nothing wrong.

"That you loved your children and you always will."

Opposition Leader Tony Abbott told the story of his former girlfriend Kathy Donnelly, who in 1977 gave birth out of wedlock to a son, whom for years Mr Abbott believed was his.

"There is no stronger bond than that between mother and child," he said.

"There are no first or second class mothers ... and every mother has the right to raise her child - we know it now and we should have known it then.

"We were hard hearted and we were judgmental, that's why we should apologise.

"We did inflict pain on those we loved."