The Human Fertilization and Embryology Bill, soon to be debated in the House of Lords, recognizes same-sex couples as legal parents and removes the requirement that IVF clinics consider the "need for a father" when evaluating an unborn child's welfare.
In a letter to The Times, the Cardinal said: "The Bill proposes to remove the need for IVF providers to take into account the child's need for a father when considering an IVF application, and to confer legal parenthood on people who have no biological relationship to a child born as a result of IVF."
"This radically undermines the place of the father in a child's life, and makes the natural rights of the child subordinate to the desires of the couple. It is profoundly wrong," he wrote.
Ben Summerskill, chief executive of the gay rights group Stonewall, said the Bill merely extends the rights already available to heterosexuals.
But the cardinal has allies among pro-family activists opposing the bill. Former Tory leader Iain Duncan Smith said the legislation would drive a "nail in the coffin" of the traditional family.
The bill also permits experiments on human-animal hybrid embryos.
Cardinal Murphy-O'Connor called on Prime Minister Gordon Brown to allow Labor members of both Houses of Parliament to have a free vote on the bill.
.- The archbishop of Westminster Cardinal Cormac Murphy-O'Connor has expressed strong opposition to a new bill making it easier for lesbian couples to undergo fertility treatment.