Almost everybody knows somebody, by sight or name, like Charlie Luker. Luker, 37, a car washer in Lawrenceburg, Tenn., works long and hard. He relaxes in front of the television with a beer most evenings, goes to bed early, gets up early and does it all over again. He is part of the backbone of the U.S. economy and society, one of the many Americans who make enough to survive but not much more.

They are little noticed by politicians and policy-makers because they do not vote in large numbers or qualify for most forms of government aid. And more affluent Americans rarely consider the life, needs or thoughts of a Charlie Luker, who shined their new cars before they drove them off the lot.

The Washington Post went looking for the one-fifth of Americans, more pervasive than visible, who live above the official poverty line but below the middle-income bracket. These are the Americans who buy used cars or no cars, take few vacations, shop for clothes at discount stores, often go without health insurance and hope for the best.

According to data in the Census Bureau's 1986 Current Population Survey (CPS) of nearly 65,000 households nationwide, this group lives in households where the annual income is $9,941 to $18,700. In two-thirds of those households, it takes two wage-earners to reach that range. The members of this group are demographically so diverse that income is one of the main statistical characteristics they share.

The other is education. Except for the senior citizens, they have less of it than the average for their age group. Throughout their lives, people with less education tend to be paid less and be unemployed more.

But in interviews, another unquantifiable similarity emerges: Those of the same age, with about the same responsibilities, expressed remarkably similar views about the future despite vast differences in their backgrounds.

The demographic analysis suggests that the members of this nearly poor quintile are white and black and Hispanic; married, single and divorced; working, retired or between jobs; old, young and in between.

Some, young and on their way up, may belong to the group temporarily. Others, ill or laid-off or on strike, are here suddenly and accidentally. Still others have wittingly chosen professions that will make them happy but not financially comfortable. And some, whose needs outstrip their skills, may be stuck here permanently.

Because living costs vary with family responsibilities, all of these people have to budget carefully, but some more carefully than others.

For example, the largest category of householders in the group (29 percent) is made up of persons over age 65 whose children are likely to be grown and gone.

And because the incomes of most people drop when they retire, senior citizens in this group tend to have done better during their working lives than the wage-earners now in the group. Many have accumulated such valuable assets as a paid-for house.

In fact, only 3 percent of householders older than 65 in the group list Social Security as their sole source of income. But when the workers in the group stop working, their incomes are likely to place them among the poorest of the poor.

The second largest number of householders in the group (24 percent) are those between 25 and 34. If they are parents, they have learned that the price of children's shoes is out of proportion to their size, but those children's appetites have not yet become the black holes of adolescence.

Of the 15 percent of householders in the group between 35 and 44, many are facing the near certainty that they will never be rich and the probability that they will not able to pay for their children's education after high school. Many others are divorced; surveys consistently find that money problems are among the leading causes of failed marriages.

The 10 percent between ages 45 and 54 are in the peak earning years for most Americans but finding it increasingly difficult to get or keep a job, especially one that would allow them to plan for retirement.

The 14 percent between the ages of 55 and 64 have reached the stage at which persons with below-average educations who have unskilled and semiskilled jobs begin to drop out of the work force. Sometimes the years of unafforable, and therefore neglected, health care play a role. For white-collar workers in the group, it is the age for hanging in there for their pensions.

Finding the Charlie Lukers of this nation -- those who fit the statistical profiles of this group in age, race, education, occupation and other characteristics -- turned out to be unexpectedly difficult. In the informal search in a half-dozen communities, few of the standard reportorial methods -- talking to ministers, priests, politicians or community, fraternal and veterans organizations -- bore fruit.

Most such community workers first said they surely knew many families whose members worked hard but earned very little. Days and weeks later, they ended by wondering where those families were. Most, it seemed, are not "joiners."

Luker said he has drifted away from his hometown buddies in Lawrenceburg over the years and was never much for church-going, voting or school. The closest the Army veteran ever got to the American Legion was a daily stop after work for a beer to go until the Legion Hall burned down in June. But a high-school acquaintance who is now a Methodist minister eventually remembered Luker and pointed him out to a reporter.

A reporter had met teacher Angela Keel, a subject of today's article on young, single adults, on a previous assignment at a meeting of the Montgomery County Day Care Council. Calls to a District of Columbia career counseling program led to Wayne Miller.

A food stamp administrator in Lawrenceburg suggested Tom Price and his family, featured in Monday's segment on young families, several years after rejecting his request for food stamps. For the same report, the reporter was led to Houston barber Ray Salinas and his family by a customer.

Local union officials led to middle-aged midwestern meatpackers for Tuesday's report. A reporter's instinct and a teachers' association led to retired Omaha teachers for Wednesday's segment. In each case, cold trails far outnumbered the warm.

Since more than 80 percent of the U.S. population is white, it is not surprising that most households in this group also are headed by white men like Luker, Census data show. But a greater proportion is headed by someone who is black, Hispanic, female, over 65 or unmarried than are households in any other quintile of the population, except the poorest.

While whites in the group are worse off financially than most other U.S. whites, the median income for all black and Hispanic households in the United States falls in this $9,941 to $18,700 range. So a group often known as "working poor" is, in this land of plenty, the middle class for blacks and Hispanics. Edward Dolbow, senior systems research consultant for The Washington Post's data processing department, contributed to this report.