LOS ANGELES — Large-scale Latin American immigration has turned Spanish into the unofficial second language of the United States. But the United States is still, in the words of one prominent sociologist, a country that is a "language graveyard" for foreign tongues. While many Americans fret over the state of their nation's primary language, there are signs everywhere that English is triumphant both at home and abroad.

As the United States strengthens its position as the world's economic superpower, the global reach of its popular culture — and English language — only grows. By mid-century, half the planet is expected to be more or less proficient in English, compared with roughly 12 percent now. Why should the U.S.-born children of immigrants be somehow immune to the rising power of the international language of diplomacy and commerce?

While immigration has powered the rise of Spanish-language media, a new demographic trend is already shifting the balance in favor of English. In Los Angeles, home to the nation's largest Latino immigrant population, Spanish-language radio stations routinely topped the charts for most of the 1990s. But the growth of Spanish-language radio leveled off the past few years.

Sometime in the 1990s, demographers say, the foreign-born portion of the Latino population reached its peak. In other words, on the basis of current projections, from now on the immigrant or first generation will be a smaller percentage of Hispanic America.

"In every immigrant experience, there is a shift from immigrant culture to ethnic American culture," said Barry Edmonston, who heads the Population Research Center at Portland State University. "Hispanics are in the middle of that shift right now."

As American Latinos now become less an immigrant market and more an ethnic market, the equation of Latinos with Spanish is beginning to fade. While slower to make the shift than other immigrant groups, Latino linguistic assimilation is not entirely unlike that of immigrants at the turn of the 20th century. According to the 1990 Census, fully two-thirds of third-generation Latino children spoke only English. And while bilingualism does persist longer within Latino families, particularly along the border region, there is no indication this precludes the use of English as the primary language.

As in past waves of immigration, the first generation tends to learn only enough English to get by; the second is bilingual; and the third tends to be English-dominant if not monolingual.

"The big picture is that bilingualism is very difficult to maintain in the U.S., and by the third generation it is extraordinarily difficult to maintain," said Richard Alba, a sociology professor at the State University of New York at Albany. "This is because English is so dominant and so highly rewarded."