Median household income in America rose to $12,686 in 1976; half of all households had more than that and half had less, according to a new Census Bureau compilation.

The 7.5 percent income increase was slightly greater than the rate of inflation: the typical family thus gained a little purchasing power. But its buying power remained about $780 below a typical household's in 1973; inflation has been that strong.

While Americans generally gained ground in 1976, the bureau said a fifth of all households had to make do on incomes of $5,405 a year or less.

On the other hand, any household with an income of $22,070 or more was in the richest fifth, and $35,000 put a household in the richest 5 percent.

Persons in the highest house hold-income groups received a far larger share of the $1.1 trillion aggregate national household income than those in the lower. The top 5 percent received $184.3 billion in aggregate household income (16.7 percent of the total), while the lowest fifth got $46.7 billion (4.3 percent). The top fifth had $484 billion, or 10 times as much as the bottom fifth.

The census report also showed:

Those stories about the highest income going to the best educated persons are true - at least in the aggregate. Households headed by persons with less than eight years of education had the lowest median incomes - $5,927 - but this figure rose steadily with more education to $13,606 for high-school graduates and education $21,932 for those with five years of college or more.

White households had median incomes substantially higher than black - $13,290 to $7,900.

Median household incomes were highest in the North Central States ($13,680), with the Northeast second ($13,070), the West slightly lower ($13,040) and the South still lower ($11,460).

By type of residence, median incomes were highest - $16,420 - in the 17 million households located in the suburbs of large metropolitan areas. About 12.2 million households in the central cities of the same large metropolitan areas had median incomes of only $10,960, while the lowest median income ($10,070) was for country farm households.

The Census Bureau said that while ostensible median incomes of households had been rising steadily for many years, real income had actually dropped each year from 1973 to 1975 because increases in income "were eroded by rising prices."

"In terms of constant, 1976 dollars, real median income had actually dropped from a high of $13,466 in 1973 to $12,481 by 1975. However, this rose to $12,686 in 1976.

In 1977, wage rates rose about 7.3 per cent, while prices rose somewhat less.

As used in the Census Bureau report, "households" means establishments made up of one or more persons, whether members of the same family or not.