A Catholic organisation says stopping gay and lesbian couples from adopting children is a form of positive discrimination.

Acting Principal Family Court Judge Paul von Dadelszen wants the 1955 Adoption Act changed to allow de-facto and same-sex adoptions. Currently heterosexual married couples and single people can adopt, but gay and de-facto couples can not.

Family Life International spokesman Brendan Malone says the law sometimes has to engage in discrimination to protect those who cannot protect themselves.

"What is in the best interests of the children concerned here? And that's where the law must always fall. It must always fail safe with the best interests of the children in mind, rather than trying to turn this into the wants of the parents."

Mr Malone says while solo parents do an heroic job under difficult circumstances, it is not the ideal.

"For a long time we thought that it didn't matter who raised kids, as long as they loved them. But we are understanding now more and more from the social sciences, children need the input of both male and female - and the loving input of both male and female."

However Judge von Dadelszen says international research shows there is nothing to show adoption by a gay couple is in anyway detrimental to a child. He disagrees with critics who insist a child needs a mother and a father.

"There will always be, in the family somewhere, a female who will be a good role model - and in reverse, in a two female family, there will be a male in the family somewhere who will be a good role model for the child."

Judge von Dadelszen says the important thing is the stability of the couple and their ability to care for a child.