Arnachism, with its bisarre mixture of utopian philosophy and ruthless violence, it again spreading in Spain - Particularly among disenchanted urban youth who reject all forms of authority.

The new breed of Spainish anarchists, who call themselves libertarians, have found a ready-made home for atopia in the reborn National Confederation of Labor and an inspiration for violence in the old Iberian Anarchist Federation.

The late dictator Francisco rushed both organizations following his victory in the 1936-39 civil war, but he failed to stamp out the deep anarchist rotts. The labor confederation had been the biggest labor union in Southern Europe before the civil war, with more than a million members.

A lot of people thought anarchism was dead," said Juan Gomez Casas, confederation leader in Madrid. He hands out membership cards to all who trudge up steps to its police-observed headquarters on Liberty Street. Membership, he said, has grown to 150,000 from 20,000 in the past year.

A writer and translator, Gomez Casas spent 15 years in Franco's prisons. He rejects violence and attributes the growth of anarchism to the confederation's "defense of alienated groups and the fact thata we don't play society's anf the government's game."

Still, he admits that some young Spaniards, inspired by the old Iberian Anarchist Federation's terroism have taken up violence to "combat the repression of the state."

The new armed anarchists, who deride the Labor Confederation, have formed a highly secretive underground called Armed Libertarian Groups. Police admit that it is active, but will not give details.

The hero of young libertarians is still Buenaventura Durruti, a violent anarchist and civil war hero whose battle cry was, "Renounce everything except victory." Posters of Durruti have become best sellers.

Spain's new anarchists are followers of the 19th century Russian revolutionary Michael Bakunin and his Italian disciples. Yet they advocate marijuana smoking and their own brand of rock music, and embarrass their elders at rallies by making love on the grass. They dress punk-style and do all they can to upset the conservative middle class.

A different kind of anarchist has revived among landless peasants in Andalusia, the mostly poor southern region of huge estates, bull-breeding ranches and sherry vineyards. This is the preacher anarchist, often self-taught, who delivers sermons claiming land and bread as communal property with fundamentalist fervor.

His current complaint is the turning of farmland into hunting preserves. Last month angry Andalusians set fire to five estates owned by the aristoeratic Domence family, one of the region's biggest landlords.

Remarked an angry anarchist, "If they won't let us farm or hunt on the land, we'll search it and burs all that's on it."

The favorite anarchist rock singer is Ramoocia, who says, "I have nothing to do with politics. I believe in total and absolute freedom." When he performs, young anarchists pack the house and - to show that they don't even respect the man they have made into a star - they throw empty beer cans at him.

Spanish authorities have ample powers to crack down on anarchists. "Few people defend us," said Juanito, 22. a Mardrid libertarian. "They think of us as punks or bomb throwers."

Juanito does not advocate violence and says he believes firmly in the anarchist philosophy that government is unnescessary and evil, and that by education and good will people can live in concord. With a group of other young anarchists, he is trying to form neighborhood "libertarian centers" to propagate the anarchist credo: "No God, no state, no boss."

Several such centers, which fly the black anarchist flag, are already operating in Catalonia, where anarchism was strongest before the civil war and is strongest today.

Anarchists have no political program. They advocate getting rid of government and replacing it with workers' assemblies to settle differences. Those who want to accelerate utopia, however, turn to violence. The impatient appear to be growing.

In the past few months paramilitary Civil Guards have arrested an undisclosed number of young anarchists in Catalonia and charged them with smuggling weapons and explosives from France with the help of exiles.

Spain's violent anarchists have been eclipsed by ETA, the Basque separatist underground, and other urban guerrillas. But utopian and violent anarchism are as much as part of Spanish history as the civil war. A psychiatrist remarked. "After 40 years of repression and lies, the young believe in nothing. So they turn to anarchism with a fervor that's religious."