Shadow home secretary David Davis has publicly sided with the Catholic Church in the row over gay adoption.
Mr Davis stressed he was speaking in a personal capacity
Mr Davis said he would "almost definitely" vote against forcing faith-based agencies to offer babies to gay couples.
But he stressed he was speaking personally and not for his party.
Senior Conservatives have been reluctant to wade into the row and party leader David Cameron stayed silent on the issue last week.
Tory MPs will be given a free vote when the new Sexual Orientation Regulations go before Parliament next month.
Mr Cameron's spokesman said he supported gay adoption but had not yet come to a view on whether Catholic agencies should be given an exemption.
But shadow attorney general Dominic Grieve said they must be able to continue their work.
He has insisted a solution can be found, despite reports of a rift with a string of Cabinet colleagues who have spoken out against an exemption.
Earlier, Education Secretary Alan Johnson said any opt-out would mean "plain, simple discrimination".
But Communities Secretary Ruth Kelly, whose department is drafting part of the new Equality Act, is a staunch Catholic and is understood to back an opt-out for church agencies.
Prime Minister Tony Blair has promised a decision in the next few days.
The head of the Catholic Church in England and Wales, Cardinal Cormac Murphy-O'Connor, has warned agencies may close rather than accept gay couples as prospective parents.
Speaking on BBC1's Sunday AM programme, Mr Davis said the right to protection from discrimination and to exercise religious views must be balanced against children's right to the best available adoption service.
"They are very badly damaged children and actually the Catholic Adoption Society is the best to do that," he argued.
Mr Davis stressed he was setting out his own view and there was "no party line" on the issue.
He said he would "almost certainly" vote against moves to deny an exemption, adding: "I think there is a better compromise available."
Mr Davis, founder of the Conservative Adoption Forum, continued: "If the consequence of this is actually we end up with a worse adoption system then that's a reason to come back to this and say perhaps this is not the right answer, we should do something else or find a better compromise."