NEW YORK — Laura Tapia is the union movement's equivalent of a beat cop.

A tiny, fast-talking woman from Puebla, Mexico, she's spent two years walking the 99-cent stores, fruit stands and sneaker shops of Brooklyn's immigrant Knickerbocker Avenue. She made her rounds recently, hugging the woman selling tamales from a cart, pointing to the car wash, which she says is usually staffed by underage kids, and clucking that the combination laundromat-Post Office was robbed in the middle of the day.

"When you are on the street all day, you know everything that happens," she said, shivering in her down parka. "Everything."

Tapia is an organizer for the Retail, Wholesale and Department Store Union. Only two of the roughly 170 stores on Knickerbocker are unionized, but organizing workers is her secondary goal. Her immediate task is investigating working conditions, injuries and wage and hour violations involving the stores' shelf stockers, cashiers and salespeople.

She's one of seven organizers working a neighborhood for the union. Their efforts, part of a small but growing push by organized labor to battle for workers who may never join a union, are as much social engineering as organizing.

Union membership has declined for 25 years in part because unions have "lost connections to communities," said Jonathan Tasini, executive director of the labor-funded Labor Research Association. Union halls, once the community centers of the urban working class, the place to find a job, a card game or a date, have all but disappeared.

"One way of thinking about how we connect to communities is thinking about doing so at the street, block and neighborhood level, as opposed to just in the workplace," said Tasini.

Work on Knickerbocker, where half the stores were union in the 1950s, "harkens back to the old days when labor unions were the centers of community vibrance," he said.

But some union advocates say small-scale community efforts aren't worth the effort; after all, unions would have to organize hundreds of thousands of workers to return to the membership numbers of the 1980s.

"In the current climate, the labor movement cannot afford to be extending resources for one or two workers at a time," said Kate Bronfenbrenner, a labor studies professor at Cornell University.

Still, unions around the country, often working in partnership with community groups, are reaching out to nonunion workers.

A new national organization, the Partnership for Working Families, pairs union research departments with community groups trying to win jobs for neighborhood workers affected by urban redevelopment projects. California unions, working with clergy, have pushed for better wages for the working poor. New York unions have assisted a campaign for better pay for nonunion restaurant delivery men.

The groups have had victories. Working with a community group in Brooklyn called Make the Road, the retail workers union has helped with civil cases and settlements resulting in more than $600,000 in back wages for workers on Knickerbocker.

The fastest-growing union in the country, the Service Employees International Union, has grown by championing the rights of underpaid janitors, security guards and hotel housekeepers. SEIU gained more than 200,000 members in two years, growing to 1.9 million as it negotiated contracts that, in some cases, doubled workers' wages. One of the union's biggest successes in 2007 was when 22,000 home care workers paid through Massachusetts' Medicaid program voted to organize. In other recent organizing drives, more than 8,000 home-based daycare workers in New York joined the American Federation of Teachers.

Jeff Eichler, coordinator of the 100,000-worker retail union's organizing project, said most union efforts are about increasing membership and then fighting for a contract for the members. The union's work on Knickerbocker is instead about identifying the union with a community.

"Only a small group of folks fight for contracts," he said. "A much greater group is highly exploited. We have to be seen as a participant with the needs and desires of the entire workforce. That leads to contract fights."

The union came to Knickerbocker after Make the Road began its back wages effort and a friend of Eichler's introduced him to the director of Make the Road.

Tapia, 38, got her start as an organizer seven years ago, after she led the union drive at the garment factory where she worked because she felt the owners were treating the elderly seamstresses poorly. She was assigned to Knickerbocker, which she walks daily from Make the Road's offices, asking every worker who will talk to her about wages and injuries.

Some victories are small. Of the two union stores on the street, one, Duane Reade, is part of a unionized chain. The union organized shoe store Footco, where some workers had been making $4.75 an hour; they now earn at least $8 hourly, with health insurance.

Other victories are larger: A 2005 settlement helped three workers win $70,000 in back wages from Big Boss Discount Inc. Joel Flores, 50, one of the workers involved in the settlement, said he had been making $300 for a 40-hour week stocking shelves outside the store in all weather.

"They exploit us," he said. "They were paying so little money."

Flores is still working at the store, which is nonunion. With the settlement, he said he built a house for his family in Mexico. Asked if he would join a union if he could, he answered, "Of course."

For Tapia, the work is a calling. "My hope is that in the future, any person who comes for work doesn't have to think or worry about their salary. They know they will be well paid. It's a human thing to get days off, personal days, sick days, benefits. It's a right."