FLORIDA is a demographic bellwether.Its population mix today - between minorities and whites, between those who speak English and those who speak Spanish, between those who earn a paycheck and those who cash a retirement check - more closely approximates what the nation's overall population mix will be at the turn of the century than any other state. How its citizens hammer out a redistricting plan promises to offer a unique window on political apportionment in the next century. And before a single district is redrawn, the big story for Florida is its net gain of four seats, from 19 to 23. The state's House delegation now moves from the seventh-largest to fourth-largest in Congress. Currently, Florida sends 10 Republicans and 9 Democrats to Washington. Just how the new lines are drawn won't be clear until next spring, say both Republican and Democratic state officials, since Florida has one of the latest redistricting schedules in the country. Conventional wisdom sees new districts going to the central and southwest parts of the state where the greatest population increases have occurred. Population shifts in Dade, Broward, and Palm Beach Counties will definitely create new district lines - and political friction. In Florida, as in many other states, the courts will play a key role. "Somebody is going to litigate," says Stan Smith, communications director for the state Republican Party. It could be the League of Women Voters, Hispanics, African-Americans, Democrats, or Republicans, he says. The last time statewide redistricting occurred, in 1982, "personal computers didn't exist," says Mr. Smith. Today, everyone can afford the hardware and software to be able "to go to a judge and say what they think is fair," he says. Under the amendment to the Voting Rights Act, minority seats must be drawn first; remaining lines then must work around that. Smith is convinced there will be a congressional district configured in such a way as to give a black candidate a good shot at electoral victory. The percentage of whites and blacks remained in balance between 1980 and 1990, with both groups growing by a rate of about 31 percent. Census figures show a 83.4 percent rise in the statewide Hispanic population over the previous 10 years. David Bositis, senior research associate with the Washington, D.C.-based Joint Center for Policy Studies, a minority issues think-tank, says it is unlikely that there will be a black congressional district in Florida. Though blacks make up 13.6 percent of the state's population, they are geo- graphically too dispersed to make this possible, he says. But there is an excellent chance there will be another Hispanic seat and that it will be Republican, says Mr. Bositis. Smith's counterpart on the Democratic side, Kathy Jurado, is confident that three new districts formed in south Florida's Dade and Broward Counties will each be Democratic and that a likely fourth district, mid-state in the Tampa area, will be Democratic as well. Democrats control both the Legislature and the state House. Some of the state's current districts are bursting at the seams. Six are 200,000 or more people above the "ideal" population for a 1992 district of 562,500. What is referred to as the "Space Coast," District 11, including Orlando and Disney World, breaks the scale with more than 900,000 people. A majority of voters in District 11 are registered as Republicans. When this district is divided, more Republicans will be registered in surrounding districts, potentially causing problems for Democrats.