Families of Hispanic origin in the United States have a median income of $12,600 a year, which means they are substantially poorer than other families, the Census Bureau reported yesterday.

The median family income in the United States is $5,000 a year more than the figure for families of Hispanic origin, according to the bureau.

The Census Bureau estimates there are 12.1 million persons of Hispanic origin in the United States.

This does not include an unknown number of illegal immigrants. Many Census Bureau experts think the actual number of U.S. residents of Hispanic origin would be higher by a couple of million, if a complete count of both legal and illegal residents could be obtained.

Of the estimated 12.1 million in the official count, 7.3 million are of Mexican origin, followed by about 1.7 million of Puerto Rican origin, 800,000 of Cuban origin and another 2.2 million of Central or South American or "other Spanish" origin.

Families of Cuban origin fare best economically, with a median family income of $15,300. This compares with $12,800 for families of Mexican orgin and $8,300 for those of Puerto Rican origin.

Hispanic-origin workers tend to hold fewer professional and technical jobs than other employed Americans. Only 8 percent held professional jobs, compared with 17 percent for workers of non-Hispanic origin.

Hispanics in the United States generally are younger than the rest of the population. Their median age is 22 years, compared with 30 years for the rest of the population, the census figures below. Only 5 percent are 65 or over, in contrast to 11 percent for other groups.

Hispanics are clustered heavily in the central cities of the nation, the Census Bureau said.

About half live in central cities, approximately 35 percent in the surrounding rings of metropolitan areas, and only one in seven lives outside metropolitan areas. This concentration in central cities in greater than any other group's.