IN this little town in the heart of lemon country between Los Angeles and Santa Barbara, sitting against the side of a white frame house in the dark, a young man from Mexico plays a guitar quietly.
The Rabelaisian sound of men laughing and singing loud a popular Mexican song comes through the wall from inside. It is the noisy camaraderie of young men away from home. It could be a camping trip or a college dormitory.
In this case, these fellows have smuggled themselves across the border from Mexico to pick citrus. The youngest, still in his teens, is on his first seasonal sojourn into el Norte. Two of the others, who look to be in their early 20s, have families of their own left behind in Mexico.
Cesar Chavez's United Farm Workers of America (UFW) is swimming against a tide of undocumented workers like the young Mexicans in this Santa Paula house. The indocumentados are difficult for the union to organize, because they fear deportation if they make waves. Meanwhile, they provide cheap and abundant competition to union pickers.
The orchards here in Ventura County produce up to half of the nation's lemon crop. The men who pick these coastal groves are not an elite among California's seasonal farm workers. (Lettuce ''stackers'' in the Salinas area are probably the highest paid.) But they have been among the best treated.
The major employers in the area, such as Coastal Growers Association and Limoneira, were pioneers in improving the terms and conditions of farm labor, and they took pains to ensure that their workers were all legal United States residents.
They still do. But these union employers here have been badly undercut by nonunion contractors.
Five years ago, during peak season, more than 3,000 of the 5,000 workers picking citrus here in the coastal orchards belonged to the UFW. Now there are less than 1,000 union members of roughly the same total.
Living standards among lemon pickers have slipped drastically, according to union organizers. Some workers are now living outdoors, they report, sleeping in cars and under the lemon trees, just as they have for years in northern San Diego County, where farm working conditions are considered California's worst.
Jose Rodriguez, the UFW's director of citrus operations for these coastal groves, figures there are 20 to 25 undocumented workers living in this average-size Santa Paula house.
Inside the side door, six young Mexicans play a high-spirited game of cards. They are sprawled in work clothes across two single beds with a low table in between. Posters have been taped across the walls and ripped off again.
Three more beds fill the room next to the kitchen, a clock radio next to the heap of clothes on one. A lemon picker's bag hangs on the door frame. These and the guitar are the only conspicuous possessions in the place.
Other young men filter through occasionally to other parts of the house as the card game progresses.
The kitchen is full of dirty dishes, some garbage is on the floor. None of the fellows here, apparently, has yet taken it upon himself to clean up.
None speaks English. All are undocumented, hence illegal.
Jose Rodriguez visits houses like this one a couple times a week, trying to organize these pickers. ''The workers want the union,'' he says, ''but they're afraid.'' What the workers fear is that if they become identified with the farm workers' union, they will either get fired or simply not get hired by the crew foremen that pick their own crews.
Although firing workers for union activity is not legal under California's unique Agricultural Labor Relations Act, undocumented workers are vulnerable to deportation if their illegal status is exposed.
Mr. Rodriguez faces other obstacles to organizing workers in the coastal orchards. Since 1980, labor contractors who hire nonunion workers to pick the trees have steadily gained dominance here.
The UFW won an election to represent pickers for Coastal Growers, the largest harvest association in the area, in 1978. Since then, the grower members have steadily slipped away from the association, leaving it a fraction of its former size. Instead, the growers pay nonunion labor contractors to pick their orchards.
Rodriguez's problem is finding an employing entity that won't slip out from under a union contract.
The growers themselves, except for a few that are already under union contract, are small and numerous. Many have groves that can be picked in a few days. So only a few of them employ a substantial number of pickers.
Other orchards are picked by several different contracting entities, and each of these crews may also work on several different properties in the course of a day.
The UFW says its difficult to define legally responsible employers. ''Growers define themselves out of existence as an employing entity,'' says Dianna Lyons, a lawyer for the UFW.
Labor contractors are even harder to pin down. So much so, notes Ms. Lyons, that the law won't recognize them as employers ''due to the fly-by-night nature of the animal.''
Because of the large pool of farm workers looking for jobs, contractors will often use them for a few days a week or a few hours a day. Sometimes the workers live in a house with the foremen, Rodriguez notes, making them even harder to organize.
So the union wants to find employers who will stick to a union contract. For that, they look to the packing sheds, where all the fruit is funneled for cleaning, classifying, and packaging. It is the packinghouse supervisors who actually have the say in assigning crews, UFW lobbyist Roberto Delacruz says.
The state Agricultural Labor Relations Board has yet to agree that packing sheds are actually employers of farm labor, but whichever way the board rules, Ms. Lyons says, its decision will be appealed to the courts.
Meanwhile, Rodriguez sees a different kind of citrus picker. Up through 1980, he saw a relatively established work force made up of men who lived here with their families and returned to the orchards every year. Many of these men have shifted to vegetables now, he says, or out of agriculture altogether. They have been replaced by a more fluid, less-experienced work force. Among these laborers , fewer have green cards that prove they are in the United States legally.