GUADALUPE, Calif. — As a nearby tractor purred to life, Miguel Villagomez picked up his knife and stepped into a furrow of dirt amid thousands of plump heads of cauliflower ready for cutting.

"This," the 19-year-old from Michoacán, Mexico, said with a touch of pride, "is my place."

For decades, the lush soil in this corner of California has been tilled largely by immigrants from Latin America, many returning year after year. But that long-standing relationship has encountered unexpected turbulence in recent weeks.

Federal authorities proposed building a processing center about eight miles away in Santa Maria for convicted criminals who are in the country illegally.

It hardly seemed a seismic event: The construction of a low-slung building on a lot currently pocked with weeds and gopher holes — a transfer station, not a detention center — where a small number of immigrants would be photographed and fingerprinted before being transported to Southern California or deported.

Officials considered it a non-event, a minor real estate deal, a blip on a planning commission agenda. But many immigrant farmworkers viewed the building as a powerful symbol of the U.S. deportation machinery, and that allowing it to be built in Santa Maria, where they have long felt welcome, amounted to a betrayal by city and federal officials.

The proposal has prompted a flurry of protests unlike any in memory here — "even in the heyday of Cesar Chavez," said Richard S. Quandt, the veteran general counsel of the Grower Shipper Assn. of Santa Barbara and San Luis Obispo Counties, a trade group.

Amid fears of street sweeps and workplace raids, hundreds of farm laborers have stepped out of the shadows, demanding that the government find another home for the facility.

Calling the proposal evidence of a disconnect between elected officials and the public, critics have launched a movement to seize more political control for Latinos and the working class. And many here say these fields have become an object lesson in the need for immigration reform.

"We have a broken system," said U.S. Rep. Lois Capps (D-Santa Barbara).

Asked about the proposed facility recently, Villagomez and his co-workers on the cauliflower lines shook their heads, shrugged and listed other places where they could find the same work: "Sacramento." "Visalia."

"If there's no people to plant, no people to cut — you're not going to see any of this," Villagomez said, sweeping his arm across a sprawling vista of fields.

That is precisely the problem, Quandt said: If Santa Maria gets a reputation as being hostile to farm laborers, the whole thing — the bedrock of the local economy — could collapse. There is a labor shortage in the California fields as it is, and reputation matters. One work crew from Salinas has already canceled plans to come in for an upcoming harvest.

"People are afraid," said Hazel Davalos, head of the Santa Maria chapter of Coastal Alliance United for a Sustainable Economy, or CAUSE, an organization that helps working families in the region.

California is the top agricultural producer in the nation; its 78,000 farms represent a $43-billion economy. This region, combined with the Salinas Valley, produces roughly three-quarters of the lettuce consumed in the United States, Quandt said.

"If you undermine agriculture, it will undermine the entire economy of the Central Coast," Quandt said. "We rely on the farmworker for what we do. We'd be nowhere without them. It's hard enough being a farmworker. They don't ask for much."

The troubles started with what local and federal officials believed was an innocuous idea: replacing a timeworn facility in Lompoc.

In the 1970s, the federal government installed a couple of trailers on the grounds of a federal prison to process immigration cases. It was supposed to be a temporary arrangement. Since then, the U.S. Immigration and Customs Enforcement agency was formed, immigration has become a critical political and cultural issue, and the agency's Central Coast enforcement office now takes custody of roughly 100 people each month.

Virtually all are "potentially deportable aliens" who have been released after serving criminal sentences.

The trailers have become dilapidated, said David Marin, office director for ICE's enforcement and removal operations. Guards can't bring cellphones in because they are on the grounds of the federal prison and phones are considered a security risk. There is no hot water.