AMERICANS are continuing to move to the Sun Belt - but the population of the industrial Midwest has started growing again. Those are some results of the Census Bureau's annual update on state population growth - ``State Population and Household Estimates, With Age, Sex and Components of Change: 1981-1988.''
The West and South continue to grow by leaps and bounds over the Midwest and Northeast, the study shows. The United States added about 19 million people between 1980 and 1988, the bureau estimates. Almost 17 million of the increase came in the South and West.
While no region suffered a net population loss, 2.2 million people left the Midwest. Most of them were from the Great Lakes states, where faltering auto and steel industries suffered plant shutdowns and huge layoffs at the beginning of the decade. The Northeast suffered a net migration loss of more than 306,000 people, all from the Middle Atlantic states of New Jersey, New York, and Pennsylvania. The two regions have gained in population because more people were born there than migrated or died.
Politicians and government officials at all levels will be poring over the statistics carefully, because they give an important preview of what the 1990 census will show. Money and political power - in the form of federal aid and grants, as well as redrawn congressional districts - will be tied to the 1990 figures.
The statistics show political power, as expressed in the US House of Representatives, following the migration to the West and South. Since there is a limited number of House seats, they must be reapportioned to the states with each census. Those states growing the most will gain seats at the expense of others.
Tom Hofeller, director of redistricting for the National Republican Congressional Committee, says the biggest winner will be California, which will pick up six or seven seats. Texas will gain two or three, and Florida will get an additional three or four. Arizona, Georgia, North Carolina, and Virginia will probably each add one seat, he says.
The biggest loser, Mr. Hofeller says, will be New York, which will probably drop three congressional seats. Illinois, Michigan, Ohio, and Pennsylvania will all probably lose two, and Iowa, Kansas, Massachusetts, Montana, and West Virginia will likely all lose one. Other possible losers include Kentucky, New Jersey, and Wisconsin.
Will this shift to the Sun Belt help the Republican Party, which usually carries those regions in presidential elections, gain control of the House?
``First, you have to look at the [presidential] Electoral College,'' Hofeller says. ``The figures are positive for the Republicans based on states they have previously carried.'' But the assumption of Republican advantage in presidential elections doesn't carry over into congressional races, he says.
Hofeller says the main reason for this is that ``demographic trends can be distorted through gerrymandering,'' or the dilution of a party's strength by clever drawing of district boundaries. Thus control of state governorships and legislatures, which will redraw congressional districts after the 1990 census, can be essential to a party's success at the congressional level.
Given current Democratic advantages at the state level, Hofeller says the situation for the GOP is critical. ``In the top 10 states, we are looking at a situation where the Republicans will be at the table with a piece of the action, or else won't be at the table at all. The Democrats will be at the table, or maybe own it.''
Howard Schloss of the Democratic Congressional Campaign Committee dismisses gerrymandering as the cause of Republican losses. ``It's a convenient excuse,'' he says. ``But the range of Democratic victories comes from all across the country. Republicans need to be more concerned about the issues and the quality of their candidates.''
Even so, Mr. Schloss agrees that the population shifts mean the 1990 state elections will be important for both parties. While he does not foresee any major change in the current balance of power at the state level, he warns that ``if Democrats take reapportionment for granted, it could have very serious consequences for the makeup of the House as far as Democrats are concerned.''
Besides the political implications, the swelling population in the West and in Florida increases the pressure on an already stressed environment. Increasing population has led to bitter disputes over water in several Western states, and many Western cities already face severe levels of air pollution.
Extensive development in Florida has endangered vital wetlands, and wildlife habitat all across the Sun Belt is threatened by human encroachment.
The states with the largest population growth in raw numbers were led by California, which grew by 4.6 million people; and Texas and Florida, both of which gained 2.6 million. In percentage terms, Nevada, Alaska, Arizona, and Florida all grew by more than 26 percent.
Four jurisdictions - the District of Columbia, Iowa, Michigan, and West Virginia - lost population between 1980 and 1988.
But a look at changes from 1985 to 1988 shows a pair of significant trends. With the economic recovery, Ohio and Michigan, both of which lost population between 1980 and 1985, have rebounded. Ohio, which lost a smaller percentage of people, actually posted a 0.8 percent gain for the 1980-88 period, while Michigan grew from a 1.9 percent loss in between 1980 and 1985 to a net 0.2 percent loss by 1988.
In addition, several states have lost population since 1985: Wyoming (a 5.9 percent loss), North Dakota (2.7 percent), Montana (2.4 percent), Oklahoma (1.8 percent), Louisiana (1.7 percent), Idaho (0.2 percent), and Nebraska (0.2 percent). In many cases, the downturn in the energy and mining industries has played a role in population decline.