Thousands of people, including families with their children, poured into a Rome piazza Saturday to protest a government bill that would give legal rights to unmarried couples, including gays and lesbians.

The proposed legislation, which awaits approval in Parliament, has been at the center of a debate dividing Italians amid calls by Pope Benedict XVI to defend the traditional family.

Hundreds of buses arrived in Rome from across Italy. A colorful crowd waving balloons, with children looking at clowns, jugglers and stilt walkers, was filling up the St. John Lateran piazza before the rally's start. Several thousand people were estimated to be in the piazza by midday.

Organizers of Saturday's "Family Day" demonstration include lay Catholic groups and family associations. While the demonstration has been endorsed by Italian bishops, neither the Vatican nor the Italian bishops' conference is formally behind it.

Nevertheless, the Italian bishops conference newspaper, Avvenire, welcomed the demonstration. "Family Speaks: A Feast for All," said the paper's front-page headline on Saturday.

Benedict sent a clear message from Brazil, where he was traveling, on the eve of the rally, assailing popular culture for promoting sexual immorality and destroying the sanctity of marriage.

"It is necessary to oppose those elements of the media that ridicule the sanctity of marriage and virginity before marriage," he said Friday. Later, he decried the "plague" of extramarital unions in a speech to the region's bishops.

The bill at the heart of the debate was passed by Premier Romano Prodi's center-left Cabinet in February.

It stops short of legalizing gay marriage — as was done in Spain and other European countries. Rather, it would entitle unmarried couples who live together to hospital visiting rights, inheritance rights and others.

"This bill is modest and it's just a partial solution," said Franco Grillini, president of the main Italian gay rights group Arcigay. "I think that the problem is that the country is scared of diversity. We need to defend the dignity of our unions, and we want the government to recognize them."

Critics, including the demonstration organizers, say the bill would dismantle what they consider to be the centerpiece of society: the traditional family based on marriage between man and woman. Supporters argue that the bill does not create an alternative family model, and say recognizing the basic rights of people who live outside marriage would make Italy more civilized.

Supporters of the bills have planned a counter-demonstration, scheduled to start at the same time as the "Family Day," in Rome's Piazza Navona — but expected to be much smaller.

The number of official marriages celebrated in Italy has declined steadily since the early 1970s, with 404,464 registered in 1971 and 264,026 in 2001 — with the number falling even further to just over 250,000 in 2005, according to the national statistics bureau, Istat.

In their place are an ever increasing number of de facto unions, which Istat estimated at about 592,000 in 2005, or about 4.1 percent of all heterosexual couples. Istat said it did not keep statistics on the number of gay couples.

As the bill awaits to be taken up by Parliament, its fate is uncertain. Prodi has left lawmakers in his divided coalition free to vote according to conscience.

Demonstration organizers say the rally should not be colored with political overtones or be seen as an anti-government protest. But the event has already proven embarrassing for Prodi's coalition, with at least one minister saying he would take part and other center-left leaders expected at the counter-demonstration.