Since Washingtonians enjoy the highest household incomes of any major metropolitan area, doesn't it stand to reason that our local charities are equally fortunate?

Not so, according to a study of philanthropy in Washington and elsewhere released by the Greater Washington Research Center a few weeks ago. Compared to six other major U.S. metro areas, the Washington area has remarkably few philanthropic resources. In consequence, our local charities receive relatively less.

Whether you look at the charitable deductions claimed by area residents on the returns they filed with the Internal Revenue Service, at the amount of giving by extremely rich Washingtonians, at the grants and assets of Washington-based foundations or at the size of charitable contributions made by big corporations headquartered here, Washington philanthropy comes out at or near the bottom. Compared with Atlanta, Boston, Cleveland, Dallas/Fort Worth, Minneapolis/St. Paul and San Francisco/Oakland, in all per capita measures of foundation giving we rank seventh out of seven. We rank last in all per capita measures of giving by our major corporations.

Depending on the per-capita measure you pick to assess the level of our individual giving, we range from below average to last on the list.

How can such an apparently af- fluent area do so poorly when it comes to charity?

The answers seem to fall into three categories. First, our potential sources of charitable giving are surprisingly small, considering the number of relatively affluent people who live here. (Remember, we're talking not just about the 600,000 residents of the District of Columbia but about the 3 million-plus residents of the entire Greater Washington area.) Experienced grant-seekers know they're most likely to get major charitable donations from very rich individuals. Yet while average Washingtonians' household incomes are high, there aren't that many mega-millionaires living here: we're outstripped by Dallas, San Francisco and Minneapolis. Our local foundations' assets and grants are very small, relatively speaking. And few major corporations are headquartered here, depriving us of a valuable potential source of philanthropic support.

Second, the charitable noise level is extremely high in Washington. Many national nonprofit groups have chosen Washington for their headquarters, perhaps because of the easy commute to Capitol Hill. Their articulate and politically savvy representatives do such a fine job in espousing their various causes that in 1980 of every dollar given to nonprofit groups located in Washington, only eight cents went to nonprofit groups with a local focus.

For the third and final set of answers we have to leave hard data and turn to the views of local philanthropic experts. These observers say many Washingtonians lack the kind of community commitment that makes residents of Minneapolis lead the seven areas in charitable deductions reported to the IRS, for example, or residents of Cleveland lead in gifts to the United Way. A test of their appraisal can be made at any local gathering of the reasonably well- to-do. Typically, few of the people present plan to be buried in Washington. Even if they've flourished here for the past 30 years, chances are most plan to be buried in Philadelphia, Pittsfield or Peoria, and whatever charitable bequests their wills contain will likely follow their remains to the remembered lands of their youth.

Or, see how many well-paid Washington professionals find that the people who pay them care whether or not they support our local community. A trade association executive serving members from across the United States is rarely under pressure from those members to give some of her earnings back to Washington. As one highly successful Washington lawyer put it, "Back in Birmingham, I could never get away with not giving to the community. But here nobody who matters to my business cares what I do for Washington. So I don't do anything."

Meanwhile, the religious institutions, hospitals, schools, social welfare agencies and arts organizations of the Washington area struggle onward, bolstered by the dedicated support of those Washingtonians, both new and old, who are committed to the welfare of our area. Based on all the data available, their ranks are relatively thin.

Our community needs our help.