VATICAN CITY - Pope Benedict ushered in the third New Year of his pontificate on Tuesday with a call for the protection of the traditional family, which he said was vital for world peace.

The Pontiff, in an apparent swipe at gay marriage, criticized policies that undermine the traditional family unit based on a union between a man and a woman.

"I wanted to shed light on the direct relationship that exists between the family and peace in the world," the Pope said, in his first public address of 2008.

"The family is the primary agent of peace and the negation or even the restriction of rights of the family ... threatens the very foundations of peace."

Gay marriage is legal in several European countries including predominantly Catholic Spain, where hundreds of thousands of people marched on Sunday in favour of the traditional family.

Unwed couples have sought more rights in staunchly Catholic countries including Italy, something Catholic leaders warn would weaken the traditional family.

Benedict, leader of the world's 1.1 billion Roman Catholics, urged followers to reject challenges to the family "darkening the truth of man".

Quoting from a message he issued in December to mark the Church's World Day of Peace on January 1, Benedict said the family was "the first and non-substitutable educator of peace".

He also said that if the world wanted to live in peace, it would need to recognize those universal values that all people share as part of a single, "human family".