With fewer children and growing numbers of both young and older Americans maintaining homes of their own, the typical household has shrunk to less than half its size when the nation was new, a Census Bureau report shows.

As of July 1, 1988, the average household included 2.62 people, a record low, the bureau reported Thursday.Family-oriented Utah was the only state with an average household size of more than three, at 3.17, the bureau reported. Florida and Oregon had the smallest average household size at 2.46.

The first national census in 1790 - an era of extended families living together - calculated that the typical household contained 5.79 people.

"More than anything else the decline in fertility" has had an impact on household size, said demographer Campbell Gibson. He said the drop in household size has resulted largely from a decline in people under age 18.

In addition, he said, larger numbers of older Americans are living on their own, as are increasing numbers of young people. Between 1980 and 1988 the total number of households increased 13.9 percent, but the population rose just 8.5 percent.

Between 1980 and 1987 the proportion of the total population under age 18 dropped from 28.1 percent to 26 percent. The nation's birth rate fell from 18.2 births per 1,000 in 1970 to 15.6 in 1987.

In recent years total births have begun to creep up again, largely because the baby-boom generation is in its prime child-bearing years. However, the baby boomers still are reproducing at a lower rate than their parents.