Faced with plummeting commodity prices and a glut of sugar on top of the disappearance of its Soviet subsidies, the Cuban government has closed about half of its sugar mills.

For the hardy field hands who endured months in the sun swinging machetes or moved nimbly in the roaring mills, this is no mere downsizing. It is the sad end of an era that was as much a part of Cuban history and culture as it was a linchpin of the economy.

The peals from a bell at the Manzanillo plantation heralded the call to arms against Spain in 1868, while the zafra, or sugar harvest, has inspired poets, singers and painters. But tourism is now Cuba's primary source of foreign exchange — bringing in some $2 billion a year, compared with about $440 million for sugar; and so, even Cuba's change-resistant authorities are bowing to the need to adapt.

"The circumstances oblige us," said Óscar Almazán, the president of Cuba's Association of Sugar Technicians. "You cannot remain in a position which is truly obsolete. We are talking about a globalized, computerized world, and you have to be prepared for this changing world. If not, you are a Jurassic Park. We are de-Jurassicizing ourselves."

Officials envision closing some 70 mills, and converting cane fields into vegetable farms or cattle ranches, while reassigning 100,000 workers to the remaining mills, other farm jobs or retraining for food processing factories.

Jorge Robert Egdhill, a welder and mechanic, has only ever worked in the mills. Now, he cuts through pipes piled outside the Aguacate mill. "It is as if a child died," he said. "To see the source of life slipping from your hands is hard. In the end, you have to do what the government says you must do. But is difficult to take apart machines you once repaired."

Like some 50 other mills across the country, the one in Aguacate had been idle for several years. National output had hovered at a shade under 4 million tons a year, about half what it was during the 1970's and 1980's when the Cubans sold sugar to the Soviet Union. (Before the 1959 revolution, similarly favorable trade with the United States fed Cuba's sugar industry.)

The deal with the Soviets meant there was no attempt to diversify crops or industrialize more fervently. Thus, when the Soviet patron collapsed in 1991 and its largess vanished, Cuba was plunged into the economic hardship euphemistically dubbed "the special period."

"The terrible thing is not that it disappeared, but that it went away at once, without any time to prepare ourselves for it," Mr. Almazán said.

As sugar mills were shuttered, officials said they began to explore restructuring and to focus on those that could burn the milled cane stalks to power electric turbines. They also studied soil to ensure that only the most fertile plantations would continue to be cultivated.

This summer, officials announced that about 60 percent of existing sugar fields would be given over to other agricultural production and that former mills would be converted to food processing plants.

Since many sugar workers have only a ninth-grade education, officials said the government is building new schools to allow them to receive a salary while studying for their high-school diplomas. Classes will include computer training, as well as vocational skills for the emerging industries, they said.

Whether there will be jobs for everyone, and whether the restructuring of the sugar industry will suffice to ease Cuba's economic problems are both uncertain, said Antonio Jorge, a professor of economics at Florida International University.

Cuba imports about twice as much as it exports, and has high debt, including loans from Russia that have yet to be renegotiated, while European companies have suspended commercial credit for nonpayment, Professor Jorge said.

"Cuba's economy is at a very crucial moment," the professor said. "It doesn't possess the capability to keep on importing and that means major crisis."

Despite official reassurances, the families residing in the batey, or mill village, nestled in the shadow of Aguacate's smokestacks are worried. There are no other jobs in the area, they said, and they are too worried about making ends meet even to think about learning a new skill.

"People older than 40 going to study, what can they do with that kind of head?" said Carmen Prieto, who lives with her husband, a tractor driver, in a narrow home that reeks of a crude oil stove. "Can you study if there is nothing to eat?"

But Noel Ibáñez, a lanky man with stubbly gray bristles, insisted that even at 58 he was not worried. He knows enough about history and sugar that he just might end up teaching in the new schools.

"The important thing is to know why we have to do this," he said. "I am not without hope. I have the guarantee of working or studying. I have the right not to be unemployed. In other parts of the world, that does not happen."

He cast his gaze upon the gigantic mill with its arched windows, broken panes and faded revolutionary slogans, and allowed himself a moment of nostalgia.

"The smell of molasses is what I'll miss," he said. "Remember, we are talking about something historic in our country."