LOS ANGELES — Like legions of immigrant farmworkers, Nancy Silva for years has done the grueling work of picking fresh fruit that Americans savor, all the while afraid that one day she could lose her livelihood because she is in the country illegally.

But the widening coronavirus pandemic has brought an unusual kind of recognition: Her job as a field worker has been deemed by the federal government as “essential” to the country.

Ms. Silva, who has spent much of her life in the United States evading law enforcement, now carries a letter from her employer in her wallet, declaring that the Department of Homeland Security considers her “critical to the food supply chain.”

“It’s like suddenly they realized we are here contributing,” said Ms. Silva, a 43-year-old immigrant from Mexico who has been working in the clementine groves south of Bakersfield, Calif.