For the 16 million black Americans who live in urban areas, New York's Nassau and Suffolk County metropolitan area may offer the best economic conditions, according to a study published in American Demographics magazine. The Washington area ranks 24th among metropolitan areas in the economic well-being of black residents, and Buffalo is last.

The study was conducted by William O'Hare, associate director for social research of the Joint Center for Political Studies, a Washington think tank on black issues. Using 1980 census figures, O'Hare ranked the 48 standard metropolitan statistical areas having 100,000 or more black residents on the basis of nine economic factors, including median household income, the rate of black home ownership and the value of black-owned homes.

An SMSA consists of a central city and surrounding suburbs or a thickly settled area such as Long Island, N.Y., where Nassau and Suffolk counties are located. O'Hare said he made some adjustments in income figures to account for differences in the cost of living.

The 48 areas contained 16 million black residents, three-fifths of the nation's black population, he said, and 27 of the areas were in the South.

O'Hare found that while blacks in northern cities usually had higher median incomes and home values, they trailed in such other measures as the ratio of black home ownership to white.

"Southern metropolitan areas in general had higher rates of black home ownership and smaller differences between black and white home-ownership rates and values," O'Hare wrote.

"Metropolitan areas outside the South had higher black incomes and home values and smaller gaps between black and white incomes."

O'Hare said that measuring home ownership as well as income is important because ownership reflects accumulated wealth and community status, and thus is "a major factor that adds to prosperity."

Overall, O'Hare rated the Nassau-Suffolk area on Long Island best for blacks in terms of economic well-being, but the next four areas were southern: Miami, Columbia, S.C., and Richmond and Newport News, Va.

Los Angeles rated seventh, the New York-New Jersey metropolitan area 19th and Baltimore 40th.

The bottom five cities were all in the northern Rust Belt: Cleveland, Chicago, Milwaukee, Newark and Buffalo.

Among the categories in which the Nassau-Suffolk region ranked first was black median household income ($18,826 in 1980). In this list, the District and nearby suburbs was second, at $16,484. The black median for all 48 areas was $11,501. In 1980, the national median household income for whites nationwide was $18,684, according to the Census Bureau.

Nassau-Suffolk also had the highest percentage of blacks owning homes, 61 percent. In this category the Washington area ranked 38th, with 37.1 percent, and the national average was 44.7 percent.

San Diego ranked highest in median value of black-owned homes, $69,100. The Washington area ranked third in this category, at $59,800.

Nassau-Suffolk also ranked first in median black household income as a percentage of white income, with 76.6 percent, while the Washington area ranked 12th at 61.9 percent.

However, in the category measuring the dollar gap between white and black median income, Tampa-St. Petersburg ranked best with the smallest dollar difference, $4,765. The Washington area was 46th, with a dollar gap of $10,130 between the incomes of whites and blacks.

Highest in black home ownership as a percentage of white home ownership was Charleston, S.C., at 86.8 percent, with the Washington area 37th at 60.5 percent.

In the ratio of black home values to white, Nassau-Suffolk was first, with blacks' homes valued at 82.4 percent of the value of whites' homes, and the Washington area ranked fourth, at 69.9.

But when the actual dollar gap between the values of black and white homes was studied, the Washington area sank to 37th, with one of the largest gaps in the nation. In the Nassau-Suffolk area, the median value of white homes was only $9,100 more than that of black homes; in the Washington area, the difference was $25,800.

Philadelphia ranked last in the relative value of black homes, which were rated at 38.7 percent of the value of white homes.

Noting that he studied only economic factors, O'Hare said, "quality of life is determined by more than economic considerations, and this analysis does not prove that Nassau-Suffolk represents the pinnacle of black America."

Other factors such as educational opportunities and the degree of racial segregation must be considered, he said.