VATICAN CITY — Pope Francis waded diplomatically into the gay marriage debate today, telling the Archbishop of Canterbury he wants to work together to promote family values “based on marriage.”

Francis, who vigorously opposed gay marriage in his native Argentina, and Archbishop Justin Welby chatted, prayed and had lunch together at the Vatican in their first encounter since both were installed in March.

Welby, the spiritual leader of the 77 million-strong Anglican Communion, has opposed legislation in Britain that would legalize gay marriage, saying it would undermine family life.

He appeared last week before the House of Lords before it moved the gay marriage bill a step closer to becoming law. The legislation would enable gay couples to get married in both civil and religious ceremonies in England and Wales.

In his remarks to Welby, Francis said he hoped they could collaborate in promoting the sacredness of life “and the stability of families founded on marriage.” He noted that Welby had recently spoken out on the issue, a reference to his House of Lords testimony.

Significantly, though, Francis didn’t say that marriage should be based on a union between a man and woman, which is how Benedict XVI and John Paul II routinely defined marriage.