WASHINGTON (AP) _ High immigration rates pose the possibility that a century from now the European whites who have dominated the nation will slip to minority status, a private population group reports.

Low birth rates among the current population, coupled with immigration estimated at 1 million annually - legal and illegal - could result in Hispanics, blacks and Asians constituting more than half the population by the year 2080, the new report speculates.

''The nation must once again redefine itself,'' reports the study, ''Immigration to the U.S.: The Unfinished Story,'' published by the private, non-profit Population Reference Bureau.

Major population changes are not unheard of in American history, a land where American Indians were succeeded by Northern European whites and black slaves. At the turn of this century Italians, Greeks, Poles and others from the south and east of Europe flooded in, vastly changing the complexion of the nation.

Today the flow stems largely from Asia and Latin America, the study notes.

''One thing is clear: The nation's ethnic composition is again changing dramatically. This is an opportunity and a challenge.''

''If illegal immigration remains high and annual immigration averages 1 million, the non-Hispanic white population would drop to just under 50 percent in 2080,'' the new study said.

The report was written by Leon F. Bouvier, a population researcher and former vice president of the Population Reference Bureau, and Robert W. Gardner, a research associate at the East-West Population Institute in Honolulu.

The 1980 Census counted 226.5 million Americans, of which 79.9 percent were whites other than Hispanics. The Census said 11.7 percent of Americans were black, 6.4 percent were Hispanic and 2.0 percent were Asians and others.

At current high immigration rates, the non-Hispanic whites could shrink to 49.8 percent of the population by the year 2080 - becoming ''the largest minority in a nation without any ethnic majority population.''

At that time Hispanics would make up 23.4 percent of the nation, having surpassed blacks as the second largest group in 2010. Blacks would be 14.7 percent of the population and Asians and others 12.1 percent.

A new immigration reform law was passed this year providing amnesty for many people who arrived illegally in the past, but imposing employer sanctions and other provisions in the hope of stemming the future flow of illegal arrivals.

Even so, economic pressures continue to build in many developing nations, with lack of jobs and prospects forcing many people to consider emmigration to other places - particularly the United States.

The challenge for the nations of Central America, in particular, is overwhelming, Bouvier and Gardner said. ''Inevitably, out of sheer desperation, vast numbers of their residents will make their way northward in search of work.''

At the same time legal and illegal immigration is maintaining high levels, the nation's birth rate is low, they note.

Since 1982 the fertility rate of American women has been below the 2.1 children per woman needed to keep the population constant over the long term.

The current rate is about 1.8 births per woman over her lifetime, which means, counting both parents, each 200 people produce only 180 offspring. Population researchers say it takes 210 children to replace 200 parents, allowing for children who do not survive to adulthood.

If immigration were to stop, at the current fertility rate the population of the nation would begin to dwindle. But the effect of the new immigration law remains to be seen.

Even if it slows illegal arrivals, those coming to this country legally will still arrive, and that also will affect the nation's makeup.

When the newcomers from Southern and Eastern Europe threatened the long dominance of Anglo-Saxon Protes tants, great concerns were expressed about the arrival of ''inferior races.''

Today racist sentiments are less blatant, and Bouvier and Gardner note that ''it is recognized that the nation has benefitted greatly from the influx of people from Eastern and Southern Europe as well as the later arrivals from Asia and Latin America. ... The United States is far better for having remained a 'nation of immigrants.'''

''The challenges of such major ethnic shifts should not be minimized, but neither should they be viewed with too many misgivings. The nation is resilient and with adequate planning any problems posed by such changes can be addressed.''