In an abrupt upward revision of past forecasts, the bureau predicts that the US population will climb more steeply in the 1990s than even during the baby-boom period of the 1950s. And it will continue to grow, increasing by 50 per cent by 2050, when the population will reach 380 million.
The higher-than-expected growth, the report says, will be attributed partly to dramatically improving fertility levels among US women - the fertility rate has already jumped from 1.8 births per woman to 2.1 births - and, more significantly, to surging immigration, legal and illegal.
The most dramatic change will be in the country's ethnic balance. Where whites of European descent now make up about three- quarters of the US population, that will have fallen to about 53 per cent by 2050, the report suggests, and Hispanics will overtake blacks as the country's second largest group. According to the report, the Hispanic population would overtake the black population in about 2013.
It is the first time that the Census Bureau has attempted a precise ethnic breakdown in its projections. By 2050, the number of Hispanics is expected to have quadrupled to about 80 million, about one-fifth of the projected population. In the same period, the number of blacks will nearly double to 62 million, or 16 per cent of the population.
The decline in the relative presence of whites - though their numbers will also rise - will make a nonsense of the current social terminology of 'majority' and 'minority' groups. 'We will have a much smaller proportion who are of European descent and what we will be calling majority or minority at that point is anybody's guess,' said Jeffrey Passel, a demography expert at the Urban Institute in Washington.
The bureau admits that its revision has much to do with new estimates of likely population influxes from abroad. Where it was once assumed that about 500,000 immigrants would enter the country annually in the forseeable future, it is now thought the figure will be closer to 900,000.
The change is partly due to the 1990 Immigration Act, which increased by 40 per cent the number of immigrants legally allowed into the US. In addition, restraints on illegal immigrants expected to stem from the 1986 Immigration and Reform Act appear to be having little effect.