"We're Moving Up: The Hispanic Migration," at 9:30 tonight on Channel 4, is an exceptionally substantial NBC White Paper on new quakes and bubbles in the old American melting pot. As a result of them, the country will go through "a time of staggering change" in the next few years, correspondent Bill McLaughlin says.

"I don't say it's a melting pot because I don't want to melt with anybody," declares one typically culture-conscious Mexican immigrant early in the 90-minute report. McLaughlin says an estimated 2 million illegal aliens from Mexico and Latin America try to get into the United States each year, and once they arrive, many become more aware and possessive of their heritage than they were in their own country.

The program, produced by Anthony Potter, explores the overlapping dilemmas that make this a truly monumental problem both for Hispanics and the country they wish to adopt. Chicago, it is reported, actually has a larger Hispanic population than Los Angeles, and has become a major port of entry for legal and illegal Latin aliens.

The U.S. Border Patrol is seen making token attempts to halt some of those who try to cross over illegally from Mexico, and there are striking night films of arrests and skirmishes; even a baby in its mother's arms raises its hands over its head when apprehended.

In addition to the immigration problems, the entry into this country of Mexican tomatoes is opposed by some -- specifically, Florida fruit growers who dislike the competition. The government has allowed the tomatoes in, one man theorizes, because "our country is so hungry for good relations with anyone in the world" right now.

There is also the matter of Mexican oil, which in recent years has further complicated the relationship between the two countries.

In Mexico, the camera visits an impoverished community where wretched refuse is a literal matter; among the few available jobs for those yearning to breathe free is work at a garbage dump. And it surveys life in a communist village where little kids are raised on foggy dreams of "revolution" and fist emblems are stenciled on all available walls.

One problem with Mexican children is that "there are too many of them," according to McLaughlin; the birth rate in the Catholic country is high. But then we meet some of the transplanted children who now live in Chicago and who tell a visiting priest what they want to be when they grow up: a fireman, a policeman, an artist. It's still the American dream, no matter what language it is dreamed in; and this report brings home the fervor and the heartache that still go into dreaming it.