MADRID - Hundreds of thousands of Spaniards demonstrated in favour of the traditional family in the centre of Madrid on Sunday, in a show of force by Catholics in what is now one of the most liberal countries in Europe.

Organisers said more than one-and-a-half million people packed Colon Square and surrounding streets for the event, which was addressed by Pope Benedict in a live video link.

While they said they had no political motives, the huge demonstration came just over two months before general elections in which a Socialist government which has legalised gay marriage and made divorce easier bids for another term in office.

Under the shadow of Colon Square's huge Spanish flag and just a short walk from the gay bars of Madrid's Chueca district, families and churchgoers bussed in from all over the country heard speakers call for the defence of the traditional family.

"Founded in the indissoluble union between man and woman, it is the place in which human life is sheltered and protected from its beginning until its natural end," said Pope Benedict.

Speakers attacked the government of Prime Minister Jose Luis Rodriguez Zapatero, who has an opinion poll lead of two percentage points over the strongly Catholic and conservative Popular Party ahead of the March 9 elections.

Spain was long one of Europe's most conservative countries, but has undergone a remarkable liberal transformation in the three decades since the death of former dictator General Francisco Franco.

Studies show Spanish social attitudes are now among the most liberal in Europe. Church attendance has fallen steeply and families are shrinking due to one of the world's lowest birthrates.

It was young, liberal voters who gave Zapatero a surprise victory in the last general elections in 2004, and many of the government's social policies have been calculated to appeal to the same demographic.

But Socialist party bosses are now worried that young people, whose wages and job opportunities have not kept pace with Spain's economic boom, might abstain rather than vote for them this March.

At the same time, liberal social policies enrage conservatives and help mobilise PP supporters, analysts say.

"These atheist, irreligious governments want to make us believe that our life has no meaning and that isn't true," said Kiko Arguello, a well-known Catholic activist and organiser of the event.