Los Angeles has its share of billionaire philanthropists and there are more millionaires in this county than anywhere else in the country. But how does the region stack up when it comes to charitable giving?

Not particularly well, at least according to one study.

L.A. County residents with incomes greater than $50,000 gave only 7.3 percent of their income, or about $4,000, to charity, according to a 2003 Chronicle of Philanthropy study. That trails New York’s 10.9 percent, as well as Houston (8.3 percent) and Chicago (7.7 percent). The national leader was Detroit, at 12.1 percent.

Among other California cities, San Francisco placed first at 9.3 percent, Long Beach next at 8.4 percent. The city of Los Angeles itself had a rate of 6.9 percent.

The Chronicle study, based on detailed analysis of deductions from Internal Revenue Service tax forms, is one of the few that tracks charitable donations by metropolitan region. It used tax data from the late 1990s; because of the cost involved, no one has conducted as broad a study using more recent data.

Philanthropy experts cite several reasons for L.A.’s poor showing nationally, including a comparative lack of religious donations, a shorter history of philanthropy, its decentralized power and social structure and a highly mobile population.

Religious charitable donations, which comprise nearly two-thirds of the volume of donations and one-third of the dollar value of all charitable giving in the U.S., tend to be strongest in the South and the Midwest. And except for Mormon-dominated Utah, they lag in most western states, according to Patrick Rooney, director of research at the Center on Philanthropy at the University of Indiana.

As an example, the Chronicle of Philanthropy cited the high level of giving to black churches as a major reason for Detroit’s top ranking in its survey.

John Ferris, director of the Center on Philanthropy at the University of Southern California, said older cities also have more established networks of social interaction, which in turn leads to giving. That helps explain why cities such as Detroit, St. Louis, New York and Minneapolis scored much higher than L.A. in the Chronicle of Philanthropy survey.

“If you’re engaged civically and socially, you’re much more likely to give,” he said.

In St. Louis, for example, a 2002 study by the center in Indiana found that higher proportions of households made charitable contributions across the board. Even 70 percent of low-income households, with incomes less than $50,000, gave to charity.

The study found that nearly three-fourths of all the charitable dollars stayed within the St. Louis metropolitan area. In Los Angeles, with its focus on entrepreneurship and large immigrant populations, there are fewer networks of social interaction, Ferris said.

The USC report found that 41 percent of residents gave no charitable contributions, compared with 31 percent nationally, while 49 percent of L.A. residents said they volunteered in the last 12 months, compared to 55 percent nationally.

But Ferris and other local philanthropy watchers say this data might be misleading. It does not include the billions of dollars that immigrants send back to their home countries each year. While most of that money goes to the immigrants’ own families, a sizable portion also goes towards physical improvements in their hometowns.