ROME - Hundreds of thousands of people, including families with their children, packed a Rome piazza yesterday to protest legislation that would give legal rights to unmarried couples, including gay and lesbian partners.

The legislation has been at the center of a debate dividing Italians. On one side are those who support calls by Pope Benedict XVI to defend the traditional family; on the other are those who say the measure would recognize the basic rights of people who live outside marriage.

The "Family Day" rally drew people from across Italy, who began pouring into the massive St. John Lateran piazza in the morning. By midday, a colorful crowd waving balloons, with children looking at clowns and jugglers, had filled the square.

Organizers put the crowd at half a million, while police estimated it at 250,000 - well beyond the 100,000 that organizers had said they expected.

"Living together is not family," said Anna Manara, 58. "A commitment such as marriage cements the bond, while other models make it easier to be together and therefore end up making it less valuable."

Organizers included lay Catholic groups and family associations. While the demonstration was endorsed by Italian bishops, neither the Vatican nor the bishops' conference was formally behind it. Nevertheless, the Italian bishops' newspaper, Avvenire, welcomed the demonstration. "Family Speaks: A Feast for All," said its front-page headline yesterday.

Benedict sent a message from Brazil, where he was traveling, on the eve of the rally, saying popular culture promoted sexual immorality and destroyed the sanctity of marriage. In a speech to the region's bishops, he also decried what he called the "plague" of extramarital unions.

The proposed legislation would not legalize gay marriage but would entitle unmarried couples who live together to such rights as hospital visits and inheritance.