Portugal's gay marriage law specifically forbids married gay and lesbian couples from adopting children.

On Monday, Portugal's President Anibal Cavaco Silva announced he would ratify the gay marriage bill approved by lawmakers in January, making Portugal the sixth European nation to grant gay couples the right to marry.

The president lamented his decision, saying he was only doing so because Social Democrats – led by Prime Minister Jose Socrates – were certain to overturn his veto.

“Given that fact, I feel I should not contribute to a pointless extension of this debate, which would only serve to deepen the divisions between the Portuguese and divert the attention of politicians away from the grave problems affecting us.”

“There are moments in the life of a country when ethical responsibility has to be placed above one's personal convictions,” he added.

Cavaco Silva, however, might have decided differently if the law allowed gay adoption. Earlier, the president attempted to derail the law by forwarding four out of five of the bill's articles to the nation's Constitutional Court. He said he did so because he doubted the bill's constitutionality. But he set aside the article that bans gay adoption, a clear signal he wanted to ensure it remained in the final legislation should the court vote in favor of the bill. The court's majority found the bill to be constitutional.

The seventy-year-old president announce his decision in a nationally televised address.

“We feel that we're experiencing a memorable, emotional moment,” Vitalinos Canas, a Socialist government MP, told Euronews. “It's a huge step for civilization, taken by our country.”

The president's signature comes just days after Pope Benedict toured the Roman Catholic stronghold of Portugal. Speaking in the city of Fatima, the pope called for a greater defense of what he said were “essential and primary values of life,” among which he included the family. He said the family was “founded on indissoluble marriage between man and woman.”

Abortion – legal in Portugal since 2007 – and gay marriage were “among some of the most insidious and dangerous challenges facing the common good today.”

The pope has taken a similar hard line in neighboring Spain, where Socialists legalized gay marriage in 2005.

Social conservatives in Mexico have denounced a gay marriage law approved by Mexico City lawmakers because it lifted a previous ban on gay adoption. The federal government has appealed to the nation's Supreme Court, saying it has a responsibility to protect children. In Argentina, a gay marriage bill that includes the right to adopt has won the approval of the country's lower chamber of Congress, but faces an uncertain future as debate begins in the Senate.

In both countries, adoption by gay and lesbian couples has stirred the most controversy.

Gay marriage is also legal in five European countries: Belgium, the Netherlands, Spain, Norway and, most recently, Sweden.

Iceland is also considering legalizing gay marriage.