About 49.6 million Americans are of English descent, more than from any other country, the Census Bureau reported yesterday.

Close behind are 49.2 million Americans of German descent, according to a special sample of people questioned in the 1980 census.

And there are about 40.2 million Americans of Irish descent, or about 12 times the current population of the Republic of Ireland, the bureau noted. About 13 million identified themselves as "American" or deriving from "the United States." Another 24 million did not provide enough information to be classified.

The 1980 census was the first in which people were questioned about their ethnic origin regardless of how many generations their families had been in America. Previous censuses went back only one generation.

After Irish, the next largest ancestry group is "Afro-American," with 21 million. It is followed by French, with 13 million.

Then come Italian, with 12 million; Scottish, with 10 million; Polish, 8 million; Mexican, 8 million; American Indian, 7 million; Dutch, 6 million; Swedish, 4 million; Norwegian, just over 3 million; Russian, about 2.8 million; Czech, 1.9 million, and Hungarian, 1.8 million.

In addition to the 8 million of Mexican derivation, another 5.5 million people are descended from other Spanish-speaking groups, such as Spanish, Cuban, Puerto Rican and the Hispanic peoples of Latin America. The total of Hispanic origin is about 13 million