NEXT NOVEMBER, 5,917 separate elections will have a major influence on the next president's relations with Congress.That's the number of state legislative seats to be filled in the fall of 1980. In the spring of 1981, those state legislators -- along with some 1,600 others already elected -- will begin drawing new congressional district lines based upon the results of next year's decennial census.

Those census results will provide few surprises to anyone who's ever heard the words "Sun Belt." The big gainers among the states, according to Census Bureau estimates, will be California, Texas and Florida. All three states will probably gain two new congressional seats. By the same estimates, Washington Oregon, Utah, Tennessee and Arizona will each pick up one new seat. With these increases, by 1982 California will have a House delegation of 45 members; Texas, 26 members; and Florida, 17 members. It would seem that the "orange-ing" of America is upon us.

All these new seats, of course, have to come from somewhere. Somewhere, in this case, is the "vote-rich industrial Northeast and Midwest" we hear so much about in election years. New York, the hardest hit of all, will probably lose four seats. Ohio and Illinois will each lose two seats. Pennsylvania, Michigan and South Dakota will each lose one seat. In South Dakota's case, that loss will represent half its entire House delegation.

The implication of these changes for future presidential elections must be disturbing for Democrats. In 1960, the three states of California, Texas and Florida had a combined total of 66 electoral votes. Since 1964, the Democratic presidential candidates have run poorly in those states. If fact, only once in the last three elections -- Jimmy Carter in Texas in 1976 -- has the Democratic nominee won a majority of the vote in any of the three states. These three states, in the 1984 election, will have a total of 94 electoral votes -- better than one-third of the 270 needed for election.

Within the states not losing or gaining seats, congressional districts will have to be redrawn to reflect population shifts. And here there is some encouragement for the Democrats and an uphill struggle for the Republicans. The Democrats will be trying to retain control of the 31 states where both legislative houses are Democratic. The Republicans, while trying to hold on the 12 states where they control both houses of the legislature, will be making a major effort because the congressional numbers are very much against them; 314 of the 435 U.S. House seats are in those 31 states controlled by the Democrats while the Republicans' 12 states include only 42 House seats.

The stakes in these legislative races are high. The movement of a district line just a dozen city blocks in a given direction can change the partisan composition of an entire congressional dirstict. New York City, alone, will very likely lose three congressional districts. It is interesting to contemplate at this moment of great national fanfare over the presidential candidtaes and talk of a Democratic or Republican sweep of Congress: many of the most important decisions may hinge on which party can recruit the best candidate to run for state represtative in Peoria or Poughkeepsie or Pottstown.