Photographs by Monica Almeida for The New York Times

Machele Sauer with her daughter Cassandra, 15, and Katie, 8.

ANAHEIM, Calif. — The Abbotts date their tailspin to a collapse in demand for the aviation-related electronic parts that Stephen sold in better times, when he earned about $40,000 a year.

He lost his job in late 2001, unemployment benefits ran out over the next year and he and his wife, Laurie, along with their teenage son, were evicted from their apartment.

They spent a year in a borrowed motor home here in the working-class interior of Orange County, followed by eight months in a motel room with a kitchenette. During that time, Ms. Abbott, a diabetic who is now 51, lost all her teeth and could not afford to replace them.

"Since I didn't have a smile," she recalled, "I couldn't even work at a checkout counter."

Americans on the lower rungs of the economic ladder have always been exposed to sudden ruin. But in recent years, with the soaring costs of housing and medical care and a decline in low-end wages and benefits, tens of millions are living on even shakier ground than before, according to studies of what some scholars call the "near poor."

"There's strong evidence that over the past five years, record numbers of lower-income Americans find themselves in a more precarious economic position than at any time in recent memory," said Mark R. Rank, a sociologist at Washington University in St. Louis and the author of "One Nation, Underprivileged: Why American Poverty Affects Us All."

In a rare study of vulnerability to poverty, Mr. Rank and his colleagues found that the risk of a plummet of at least a year below the official poverty line rose sharply in the 1990's, compared with the two previous decades. By all signs, he said, such insecurity has continued to worsen.

Top, she shops for groceries with Katie, 16 months; at right, she and her daughters in their mobile home. Ms. Sauer waitresses at night while her husband is in prison; she wants to go to nursing school.

For all age groups except those 70 and older, the odds of a temporary spell of poverty doubled in the 1990's, Mr. Rank reported in a 2004 paper titled, "The Increase of Poverty Risk and Income Insecurity in the U.S. Since the 1970's," written with Daniel A. Sandoval and Thomas A. Hirschl, both of Cornell University.

For example, during the 1980's, around 13 percent of Americans in their 40's spent at least one year below the poverty line; in the 1990's, 36 percent of people in their 40's did, according to the analysis.

Comparable figures for this decade will not be available for several years, but other indicators — a climbing poverty rate and rising levels of family debt — suggest a deepening insecurity, poverty experts and economists say.

More people work in jobs without health coverage, including temporary or contract jobs that may offer no benefits or even access to unemployment insurance. Medicaid is offered to fewer adults (though to more children). Cash welfare benefits are harder to secure, and their real value has eroded.

About 37 million Americans lived below the federal poverty line in 2004, set at $19,157 a year for a family of four. But far more people, another 54 million, were in households earning between the poverty line and double the poverty line.

"We don't track this group of people, and they are very vulnerable," said Katherine S. Newman, a sociologist at Princeton University who studies low-end workers.

Those suffering a nose-dive say the statistics do not begin to convey their fears and anguish.

Only a year ago, Machele Sauer thought she was entering the middle class. She and her husband, a licensed electrician, owned a large mobile home. He was starting his own business and Ms. Sauer, after bearing their fourth child, hoped to stop waitressing and be a stay-at-home mom.

"We were the ideal family, the envy of others," she said recently as she collected free food and diapers at the Hope Family Support Center, a small charity in Garden Grove, Calif., in Orange County. "And then, boom, everything flipped upside down."

Life fell apart last spring when her husband was arrested on theft charges, linked to a recent drug addiction she says she did not know about. Because of a prior record, he received a long prison sentence.

Now Ms. Sauer, 34, draws on the charity for goods and its director, Gayle Knight, for advice and emotional support, part of a grueling scramble to provide for her four daughters, ages 16 months, 8, 9 and 15. Many days over recent weeks, she dropped them at the baby sitter after school, worked the night shift as a waitress, picked up the sleeping children after midnight then woke up with the baby at 6:30 a.m. before preparing the older three for school.

At first she went on welfare, receiving $600 a month along with paid child care and counseling for herself and the children. As she resumed waitress work—four night shifts and two day shifts a week—she earned about $1,300 a month, which led her welfare payment to be cut to $300.

She receives $200 worth of food stamps that cover bills for just the first two weeks of each month, she said.

"Now the van is breaking down," she said. "With four kids it's really hard to hold a full-time job, and I need to make sure they do well in school." Her goal is to find a way to prepare for nursing school. Skip to next paragraph Enlarge

The Abbotts, too, sought aid from food banks and other charities, collecting weekly boxes of food and toiletries.

In Orange County, about 220,000 people received food from 400 local charities last year, according to the Second Harvest Food Bank, which distributes donations. Recipients include many families, often Hispanic, with several children and both parents working minimum-wage jobs. Over all, half the families seeking food had at least one working adult, according to a recent study by the food bank.

In the center of Orange County, a world away from its polished coastal towns, borderline poverty is common but seldom visible. On small streets behind strip malls and fast food restaurants, families, sometimes two of them, cram into small, aging bungalows.

What look like tourist motels along Beach Boulevard are mostly filled by working families or single people who stay for months or years, paying high weekly fees but unable to muster up-front money for an apartment rental.

Mr. Abbott, now 58, eventually found a lower-paying sales job. With help from church members, the couple amassed the three months' rent of $2,700 required to rent a one-bedroom apartment in Anaheim.

Describing their last several years, Mr. Abbott kept circling back to the emotional toll. Motels, like the one they lived in for eight months for $281 a week, are "dives," he said, "with lots of screaming and fighting and cops being called."

"It was really stressful," he said, "and still you pay a lot of money."

In a new setback, Mr. Abbott has developed chronic obstructive pulmonary disease. He recently had to stop working and go on state disability, which pays $1,436 a month and gives him health coverage.

Ms. Abbott has no health insurance — if she gets sick, she says, she will go to a medical van that serves the homeless. But a generous dentist from church helped her get new teeth, and now she plans to hunt for work.

Copyright 2006 The New York Times Company. Reprinted from The New York Times, National, of Monday, May 8, 2006.