With the economy beginning to slow, the current expansion has a chance to become the first sustained period of economic growth since World War II that fails to offer a prolonged increase in real wages for most workers.

The median hourly wage for American workers has declined 2 percent since 2003, after factoring in inflation. The drop has been especially notable, economists say, because productivity -- the amount that an average worker produces in an hour and the basic wellspring of a nation's living standards -- has risen steadily over the same period.

As a result, wages and salaries now make up the lowest share of the nation's gross domestic product since the government began recording the data in 1947, while corporate profits have climbed to their highest share since the 1960's. UBS, the investment bank, recently described the current period as "the golden era of profitability."

Until the last year, stagnating wages were somewhat offset by the rising value of benefits, especially health insurance, which caused overall compensation for most Americans to continue increasing. Since last summer, however, the value of workers' benefits has also failed to keep pace with inflation, according to government data.

Economists offer various reasons for the stagnation of wages. Although the economy continues to add jobs, global trade, immigration, layoffs and technology -- as well as the insecurity caused by them -- appear to have eroded workers' bargaining power.

In Europe and Japan, the profit share of economic output is also at or near record levels, noted Larry Hatheway, chief economist for UBS Investment Bank, who said that this highlighted the pressures of globalization on wages. Many Americans, be they apparel workers or software programmers, are facing more comptition from China and India.

In another recent report on the boom in profits, economists at Goldman Sachs wrote, "The most important contributor to higher profit margins over the past five years has been a decline in labor's share of national income." Low interest rates and the moderate cost of capital goods, like computers, have also played a role, though economists note that an economic slowdown could hurt profits in coming months.

For most of the last century, wages and productivity -- the key measure of the economy's efficiency -- have risen together, increasing rapidly through the 1950's and 60's and far more slowly in the 1970's and 80's.

But in recent years, the productivity gains have continued while the pay increases have not kept up. Worker productivity rose 16.6 percent from 2000 to 2005, while total compensation for the median worker rose 7.2 percent, according to Labor Department statistics analyzed by the Economic Policy Institute, a liberal research group. Benefits accounted for most of the increase.

"If I had to sum it up," said Jared Bernstein, a senior economist at the institute, "it comes down to bargaining power and the lack of ability of many in the work force to claim their fair share of growth."

Nominal wages have accelerated in the last year, but the spike in oil costs has eaten up the gains. Now the job market appears to be weakening, after a protracted series of interest-rate increases by the Federal Reserve.

There are two economies out there," Mr. Cook, the political analyst, said. "One has been just white hot, going great guns. Those are the people who have benefited from globalization, technology, greater productivity and higher corporate earnings.

"And then there's the working stiffs,'' he added, "who just don't feel like they're getting ahead despite the fact that they're working very hard. And there are a lot more people in that group than the other group.