EARLY in the 21st century, if projections hold true, Hispanics will become the largest minority group in the United States, surpassing blacks. On a tide of immigration, the Hispanic population in the US rose 53 percent during the 1980s, in contrast to growth rates of 6 percent for whites and 13 percent for non-Hispanic blacks. Like other immigrant groups, Hispanics are tugged in two directions by a desire to participate fully in the American experience and, at the same time, a wish to preserve their language and cultures. Even as they experience these buffeting forces, however, Hispanics are moving inexorably into the American mainstream, as both their economic prowess and political clout increase. Despite obvious similarities in their experiences in the US, Hispanics are actually a community of communities, reflecting their many nations of origin. Mexican-Americans are concentrated in the Southwest, Cuban-Americans in Florida, and Puerto Ricans and Dominicans in the Northeast. In a special four-page report today starting on Page 9, Monitor reporters take a look at these communities. It is part of a series of special reports on America's largest minority groups. A report on black Americans appeared March 8. A look at Asian-Americans will appear this summer.