PARTLY as a result of reforms undertaken in the 1960s, the United States is currently experiencing the largest sustained wave of immigration in its history.  Each year, the United States admits between 700,000 and 900,000 legal immigrants; additionally, the Immigration and Naturalization Service estimates that 5 million illegal aliens now live in the country, with 400,000 new illegal aliens settling here annually. This influx of legal and illegal immigration has caused the foreign-born share of the population to double from roughly 5 percent of the population in 1970 to 10 percent today. ‘While less than the 15 percent recorded in 1910, the 27 million immigrants now living in the country is more than twice the 1910 number.