"May we all continue to preach that Gospel of life by our words and by our actions –- as we value more and more life unborn, life unfulfilled, and life usurped in our own journeys towards life unending in the company of our Risen Lord Jesus Christ," he said in the homily prepared for the faithful gathered in St. Mary's Cathedral.
He described a recent Parliamentary report on embryo research as a "development which would lead to even more destruction of human life."
The cardinal added: "At this present time there is a growing debate in our country -- not about the teaching of the Catholic Church with regard to ending abortion completely, but rather as to whether or not there should be a reduction in the time limit for abortions from 24 weeks to 20 weeks.
"It is apparent that the moral values of our entire society are called into question by the practice of abortion -- because it is permitted, our laws and medical practice conspire to debase the value of human life and contrary to all logic to allow life at its most defenseless to be attacked and destroyed."
"While I appeal for the ending of all abortion," Cardinal O'Brien said, "I acknowledge with Pope John Paul II that it is indeed legitimate to make an imperfect choice where the object of that choice is the preservation of the lives of unborn aged between 20 and 24 weeks and so I endorse moves to bring about such reductions."
The cardinal also referred to the U.S. case of Terri Schiavo.
"Life is, of course, equally vulnerable as one approaches death," he said. "Again in recent days we have seen the case of the brain-damaged American woman Terri Schiavo whose parents have filed an emergency appeal to the U.S. Supreme Court, as they fight to keep their daughter alive. Mrs. Schiavo, had her feeding tube removed last week, and is currently dehydrating and starving to death as legal battles rage around her.
"Earlier this week, Bishop Elio Sgreccia, president of the Pontifical Academy for Life, said this action, was 'an illicit and grave act not only on the fact that food has been taken away from her, but also on the decision that tries to legitimize such a thing.'"
Across the Atlantic, in Florida, Schiavo's family appeared quietly resigned today to watching their daughter die.
With their legal options gone, they asked protesters to spend Easter with their families as the brain-damaged woman went a ninth day without food or water.
Back in Britain, meanwhile, Cardinal Cormac Murphy-O'Connor, the archbishop of Westminster, compared abortion in Britain to the eugenic practices of Nazi Germany.
Writing in the Telegraph newspaper today, Cardinal Murphy-O'Connor, deplored "[the] terrible truth that it is the strong who decide the fate of the weak."
He added: "Human beings therefore become instruments of other human beings. That way lies eugenics, and we know from German history where that leads.
"We are already on that road: for what else is the termination of six million lives in the womb since the Abortion Act was introduced, and embryo selection on the basis of gender and genes?"