Another force pushing Americans to delay retirement is that the percentage of companies that provide health coverage to retirees is half what it was two decades ago. Moreover, the age to obtain full Social Security benefits has increased to at least 66 for people born after 1942, from its traditional 65.

The median income for those 65 and over was just $18,208 in 2008  a quarter of them had incomes under $11,139, according to Patrick Purcell, an expert on older workers and pensions with the Congressional Research Service.

The average Social Security recipient age 65 and over receives just $12,437 in annual benefits, he said, and among individuals 65 and older who received income from financial assets, half received less than $1,542 last year.

While Social Security keeps most seniors above the poverty line, there are a substantial number near poverty “who are just getting by,” said Richard W. Johnson, a senior fellow at the Urban Institute. Many economists say it is good that Americans are working later in life  many are living longer and able to contribute longer.

Still, many older job seekers insist they are losing out because of age discrimination. Last year, nearly 25,000 workers filed age discrimination complaints, a 29 percent jump over 2007, according to the Equal Employment Opportunity Commission.

“I often get told that I’m overqualified,” said Barbara Brooks, 71, who retired in 2003 after 30 years as an administrative assistant at the University of California, Los Angeles. She said being told that is code language for “you’re too old.” But Ms. Brooks said she wanted to work  and needed to  citing her monthly mortgage of $1,500, which eats up half her monthly pension.