THE DEMOCRATS have survived redistricting. Despite the opportunities created by a reapportionment that shifted 17 seats from the Frost Belt to the Sun Belt and many more from center-city to suburb, the Republicans have come up almost empty-handed.

That fact -- acknowledged by districting experts in both parties -- dims the GOP's chances in the midterm November election and gives the Democrats a political dividend they really did not expect.

"We have won the reapportionment battle of 1981-82," Democratic National Chairman Charles T. Manatt proclaimed last week. A consensus estimate is that Republicans probably will have lost a net of three or four seats, and Democrats gained as many, when pending court cases settle the lines in Georgia and New York, the last two states still pending.

New York, the biggest loser in the reapportionment dictated by the 1980 census figures, drops from 39 to 34 seats. A plan designed by the state legislature would have cost the Democrats three seats, the Republicans two. But that plan was upset by the Justice Department on Tuesday, and the primary has been pushed back nine days, to Sept. 23, to allow the courts and legislature more time to straighten out the situation.

A federal court last week told a court-appointed master to draw up modifications of the legislature's plan while the legislature is negotiating with the Justice Deparment. The department said that a "meandering and convoluted" Brooklyn district appeared designed to dilute black voting strength.

A similar objection to the "dilution" of black strength in the Atlanta area has kept Georgia authorities in court and Georgia candidates in a frenzy of uncertainty about their lines. Two seats -- both now held by white Democrats -- could be affected by the outcome of this battle, with the GOP hoping the final plan will increase chances of electing one center-city black Democratic congressman and one suburban white Republican.

As these examples indicate, the courts have been heavily involved in arbitrating the conflicts between the parties and between competing racial and ethnic groups this year.

In close to half the states, federal or state courts have intervened, either drawing redistricting plans themselves or issuing standards the legislative linesmen have to meet.

Republicans blame the courts for most of the reverses they've suffered. When redistricting began, GOP officials predicted a net gain of a dozen seats from the process -- almost half of what they would need to gain a majority in the House for the first time in 28 years. Instead, according to one of the same officials, who declined to be identified, they have found themselves the victims of "judicial gerrymandering."

Among the examples they cite are these:

* In California, where Rep. Philip Burton (D) designed a classic gerrymander that was pushed through the Democratic-controlled legislature, the voters in a June 8 referendum voided the plan by a 2-to-1 margin.But the state supreme court, dominated by appointees of Democratic Gov. Jerry Brown, had already ruled that the Burton plan would stay in effect for 1982.

* In New Jersey, outgoing governor Brendan Byrne approved a Democratic redistricting plan on the last day before he yielded office to a Republican. That plan was so blatant in its gerrymandering that a three-judge federal court found it unconstitutional. But New Jersey Democrats obtained a stay order from liberal Supreme Court Justice William J. Brennan, which kept the districting plan in effect for this year.

* In Michigan, when Republican Gov. William G. Milliken vetoed the Democratic legislature's plan, the Democrats stalemated a new bill, then went judge-shopping and wound up in a Detroit federal courtroom where the vetoed Democratic plan, with one minor variation, was approved.

* In Minnesota, where a similar deadlock occurred between the Democratic legislature and the Republican governor, a three-judge federal court split on party lines, 2 to 1, in drafting a plan very favorable to the Democrats. The two Democrats (one of them a former member of the Democratic National Committee) approved a radical restructuring of the state, which forced Rep. Tom Hagedorn (R) to move out of his territory to avoid a collision with Rep. Vin Weber (R), then forced Rep. Arlen Erdahl (R) to move into a new district to avoid a showdown with Hagedorn. It also weakened a fourth Republican, Rep. Arlan Stangeland.

Appeals are pending from several of these states, and from others as well. The likelihood is that the Supreme Court next year may have to lay down some clarifying guidelines for its one-man, one-vote decision. Almost certainly, many states will go through another round of redistricting battles.

But for now, the Democrats are celebrating an unexpected political boon. Their only serious setbacks came in Indiana and Pennsylvania, where Republicans controlled the redistricting process and Democrats took a pair of two-seat losses. But those were offset by two-seat GOP losses in New Jersey and Illinois.

Even more telling is the picture of what happened in the growth states, where Republicans were expected to reap a bonanza. The GOP is favored for single-seat gains in Arizona, Colorado, Nevada, Oregon, Utah and Washington. But in the big winners -- Florida, Texas and California -- Democrats are expected to make a net gain of nine seats, and Republicans none.

That is principally because Democrats control the legislatures in those three states and hold the governorships in all but Texas. There are places where Republicans had that advantage -- notably Illinois -- and blew it by letting the fight get into court. But the Democrats, as the saying goes, "seen their chances and took 'em."

Reacting a bit defensively to charges that the GOP was outthought and outmaneuvered in the districting battle, one Republican National Committee official said the party was mostly the victim of exaggerated expectations.

In 1981, Republican publicists spread the word that with money to burn and the most sophisticated computers to employ, the party was on the verge of wiping out the Democrats' long-term dominance of the House.

But that was never in the cards, GOP districting experts now maintain. Democrats completely controlled the process in 17 states with 162 House seats; Republicans enjoyed equal leverage in only eight states with 53 seats. The other 25 states had split control, and many of them ended up in court.

Perhaps as big a surprise as the Democrats' escape from doom was the lengths to which both courts and legislatures have gone to protect urban and minority-group representation.

When the Census published its 1980 figures, the 25 lowest-population congressional districts were clustered in central cities. All were held by Democrats, 11 of them black and one Puerto Rican.

Pending final action in New York, none of those districts have been wiped out. Instead, the borders have been moved out far enough to bring them up to population equality standards without jeopardizing the incumbents. Redistricting was not a factor in the defeat of one white from Chicago and the retirement of one black from New York. The others are expected back.

Hispanics will certainly gain in numbers. Two districts in California, one in New Mexico and one more in Texas were drawn to favor Hispanic candidates, and there may be better chances for electing additional Hispanics in New York and Florida under new lines as incumbents retire.

Demographic patterns will almost certainly increase the number of black representatives from Northern cities as the 1980s unfold, even though that number is likely to be static in 1982.

Blacks complained that districting decisions were adverse to their chances of gaining seats in such Southern states as Alabama, Georgia, Louisiana, Mississippi and North Carolina. They lost their battles in Alabama and Louisiana; Georgia is stil unsettled.

In Mississippi, the protracted court battle may or may not have produced a victory for blacks last week. When the Supreme Court affirmed a new plan, creating a majority-black district in the Delta, incumbent Rep. David R. Bowen (D), who is white, announced he would not seek reelection. Both black and white candidates are expected to file to succeed him, and the 54 percent black population is not considered high enough to guarantee a black victory.

Earlier, Justice Department objections scuttled a North Carolina plan that kept Durham County, with a politically potent black community, out of the district of Rep. L. H. Fountain (D). When the legislature put Durham County into the district, Fountain decided not to seek another term. A black candidate is given a good chance in next week's Democratic primary, but could face problems in a runoff.

These examples illustrate the basic point that line-drawing is the start, and not the finish, of the campaign. After every past census, experts in both parties point out, Republican candidates have grabbed districts that were drawn to favor a Democrat, and vice versa.

Republicans have a better-than-expected chance to win a "Democratic seat" in California, because Rep. John H. Rousselot has moved into the open district. Democrats are favored to win a "Republican seat" in Ohio, because Rep. Dennis E. Eckart shifted over to take advantage of a Republican incumbent's retirement. Races in Massachusetts, Missouri, South Dakota and New York, where incumbents of opposite parties are in the same district, will clearly be shaped by the relative strength of the candidates.

Nonetheless, there is little doubt that, overall, the Republicans have failed to capitalize on their much-heralded redistricting advantages.