MADRID – Shortly after his election in 2004, Socialist Prime Minister Zapatero ended a quarter-century of cozy church-state relations by blocking mandatory religious classes in public schools. He then took wider aim, saying his government would relax abortion laws, ease restrictions on divorce, legalize gay marriage, and permit gay couples to adopt children.

In response, the archbishop of Madrid called the Spanish capital “a hotbed of sin.” Pope John Paul II accused Mr. Zapatero of “promoting disdain towards religion” and said the Catholic Church in Spain would never yield “to the temptation to silence it.”

Things got particularly nasty when the press joined the fray. A radio station sent reporters into confessionals with hidden microphones and broadcast unsuspecting priests warning against the evils of birth control, homosexuality, and surfing the Internet.

Two months ago, a disc jockey from an anti-government, church-owned radio station in Madrid posed as Mr. Zapatero and called Bolivia’s socialist president-elect, Evo Morales, to congratulate him for joining the Cuban-Venezuelan leftist “axis.” Mr. Morales fell for the gag, leading to red faces all around.

With exchanges like these, the battle between the church and Mr. Zapatero’s government has spread from parliament to streets, pulpit, and confessional, creating some of deepest political and social schisms in Spain since it returned to democracy 28 years ago.

“This is a government that is deeply secular and reform-oriented,” a government spokesman, Fernando Moraleda, said, arguing that Spain needed to adapt to its position as a modern member of the European Union. “We can’t allow Catholic doctrine to be superior to the government and the government’s legitimacy.”

Church supporters say Mr. Zapatero’s government is simply anti-clerical – as socialists traditionally are in Spain – and out of touch with Spanish society, which is more than 80% Catholic. They accuse the government of toying with a carefully crafted constitutional balance between church and state that has helped keep Spain peaceful and democratic since the death of the longtime dictator, General Francisco Franco, in 1975. Clashes between the Spanish left and the church helped propel Franco to power during the 1936-39 civil war.

“The situation today comes from this government breaking with the consensus of the past. The peaceful, democratic transition” that followed Franco “has started to fracture,” a political and sociology professor at Madrid’s Complutense University, Carlos Corral Salvador, said.

Government backers say the opposite – that the church is out of step with Spanish society, as evidenced by surveys in which four out of five Spaniards call themselves Catholic but half of those say they are non-practicing. Conservative church leaders are refusing to modernize, government sup porters say, and are struggling to retain their influence not only with the government but with moderate, younger priests and a flock that is demanding liberalization.

“It is an internal battle of the church, between bishops who were appointed by the Polish pope who are against modernization and who are very conservative, and other priests who are more modern and have less voice,” the president of Sociologists Without Borders, Alberto Moncada, said, referring to John Paul, pontiff from 1978 until 2005.

Mr. Zapatero “is doing what the people want, what he was elected to do,” Moncada said. “The church is watching its influence shrink in the minds of young Spanish people, and it wants to preserve its old privileges. This is about survival and power.”