There were slam-bang primaries in two southern states this month -- North Carolina and Texas.

Candidates said nasty things about one another, saturated the airways with millions of dollars in television ads, and so thoroughly dominated the headlines that the other party's primaries got all but lost in the din.

Politics as usual in the one-party South?

Not exactly: This time, all the big-time politicking was not in the Democratic, but in the Republican primaries.

That's never happened in the post-Reconstruction South before, and it speaks volumes about how far the GOP has come since the days when, as a Mississippi Democrat once put it, "the only thing that protected Republicans was the game laws."

Today, Republicans are the moving party in the South. They are waging statewide primaries, recruiting candidates for local offices once deemed off-limits, enticing voters and elected officials to switch parties, and leap-frogging ahead of Democrats in political technology and fund-raising.

If their advances were merely the byproduct of one man's extraordinary popularity -- President Reagan's approval rating among southern whites stood at 82 percent last month, according to a survey by The Washington Post -- Democrats might simply hunker down and mark 1988 on their calendars as the year of the firebreak.

To be sure, that is a critical ingredient. Capstone Polls taken in Alabama from 1981 to 1986 show a direct correlation between Reagan's popularity and the growth of those identifying themselves as Republicans.

But forces larger than Reagan's popularity among southerners are at work. Migration, cultural homogenization, urbanization, growth, racial progress -- all these tides threaten to wash away the foundations of a one-party system that has prevailed in this region, and in this region alone, for a century.

As potent as these forces are, their political consequences are not set in stone. The demographic changes have not taken hold uniformly throughout the South, nor do they, in and of themselves, guarantee an end to Democratic hegemony.

Even now, while their dominance has been eroding slightly, Democrats control 78 percent of all state legislative seats in the states of the Old Confederacy -- perhaps the best index of grass roots political strength.

Moreover, in the poorer states in the South -- Mississippi, Alabama and Arkansas -- the GOP has been able to win some statewide races and congressional seats in the past two decades, but it remains essentially inert at the local level. Here, Democrats have become the party of reform, or of youth, or of progress; they have have remade their party without yielding control. And to the extent that there has been a Republican threat, it has, like a good hanging, served to concentrate the Democrats' minds. "All I have to tell office-holders is that Republicans don't want but one thing -- your job," says Georgia State Democratic Chairman John Henry Anderson, who predicts a big Democratic win in state and local elections this year.

In other states of the South -- Tennessee and Virginia come to mind -- Republicans had seemed poised to establish grass-roots dominance a decade and a half ago, only to find themselves unable to sustain the momentum because of inattention to party-building (in Tennessee) or because (in Virginia) Democrats managed to recapture the governor's mansion by silencing their liberal elements.

And even in those states where the GOP thrust seems stronger -- Texas, Florida, the Carolinas -- it is by no means inexorable. In North Carolina, this month's hard-fought GOP Senate primary victory of Rep. James T. Broyhill over David Funderburk exposed party fissures that raised questions about the stability of the Republican "majority" coalition in the South. Can traditional mountain Republicans, who are economic conservatives and social and cultural liberals, and New Right low-country Republicans, who are economic liberals and social conservatives, stay together over time? Can "high-church" Episcopalians live in the same party with "low-church" Baptists? It is not clear.

What is clear is that this battle for the soul of the party is raging throughout the South. This spring in Virginia, in the aftermath of the statewide Democratic sweep of 1985, traditional conservatives ousted New Right conservatives from control of the Fairfax County GOP. "We had a cancer, we had to cut off a leg," explained state legislator Robert T. Andrews (R) of McLean. Meantime, in Virginia Beach, exactly the opposite happened: Forces allied with fundamentalist Rev. Carl Bieber ousted the traditional GOP city chairman, and Bieber subsequently became 2nd District GOP chairman.

"Republicans have inherited the disease of the Democrats, killing one another," said Richard Scherr, a University of Florida political scientist, noting the coastal-inland factionalism that has long bedeviled the GOP in his state.

In Florida, the GOP, though ascendant, has had other problems as well. A series of embarrassments in the 1970s during the administration of GOP Gov. Claude Kirk Jr. probably set the GOP surge back a decade. It also served as a reminder that, in politics, individuals do make a difference -- for better or worse. The same lesson looms in Alabama, where Gov. George C. Wallace's decision to remain a Democrat, rather than join Sen. Strom Thurmond's (S.C.) conversion to Republicanism, has held the GOP back at least a generation, perhaps more.

And Texas, with its booms and busts, offers a reminder of the fickle role the economy sometimes plays in partisan shifts. The election, in 1978, of the state's first GOP governor in a century was followed by a big Democrat comeback in the recession year of 1982 when Gov. Mark White was elected. And now, in 1986, that Republican ex-governor, William Clements, is himself trying to come back, his fortunes boosted by the dropping price of oil. He had a big primary win earlier this month.

Texas was also the scene last summer of a $1.5 million GOP effort to pick off a congressional seat in the rural, heavily Democratic First District in a special election. The Republicans missed by a percentage point -- but a big miss it was. This year, no GOP candidate is running against first-year incumbent Rep. Jim Chapman (D-Tex), and Republicans have had trouble recruiting quality challengers in congressional districts throughout the rural South. The Texas special election was to have been their big breakthrough. "If they'd won that seat, most of our incumbents . . . in the South would be facing tough challengers today," said Rep. Tony Coelho (D-Calif.), chairman of the Democratic Congressional Campaign Committee.

Despite this mixed picture, those two GOP primaries in Texas and North Carolina tell a powerful tale. A flashback to 1952 for a story Sen. Paula Hawkins (R-Fla.) likes to tell helps to understand just how much they signify in this "one-party" region.

She was a young housewife newly arrived in Florida, and she went to the courthouse to register as a Republican. The registrar took her aside to explain the facts of life. In the South, he told her, if you register Republican, "you won't get to vote" in the only local and state elections that ever decide anything -- the Democratic primary.

That wasn't merely a partisan sales pitch. It was -- and, in the rural areas, it remains -- the most salient truth about local southern politics in this century. It has also been a self-perpetuating truth: If there aren't any local Republican candidates, nobody bothers to register Republican; so nobody builds the party; so there are no Republican candidates, so . . .

Today, that cycle is beginning to crack. In retrospect, what's remarkable is how long it has taken.

For a generation now, the South as been voting more Republican than the rest of the nation in presidential races -- drawn to the party that has offered itself as a bulwark against against taxes, inflation, communists, social engineers and moral decay. At the same time, however, southerners have continued to vote more Democratic than the rest of the nation at the local level -- in part out of habit, in part because the South is the natural home of populism, and here the word "Republican" still carries the faintly malodorous connotation of "elite" and "wealthy" and "not us."

On Election Day of 1984, this dichotomy had an unlikely result: President Reagan carried 109 of the 116 southern congressional districts, while Democratic congressional candidates carried 73 of those same 116 districts, and Democrats captured 78 percent of all state legislative seats in the South. Reagan is even more popular in the South than he is in the rest of the country.

This regional split-level habit of voting is without precedent in American political history. The same pattern, in less extreme form, also shows up throughout the country. Democrats have controlled the House of Representatives for 32 years, a modern record, while Republicans have lived in the White House for 20 of those 32 years. Again, that is unprecedented.

These figures make a persuasive case that what has been taking place in the South (and to a degree, in the whole country) is not realignment but dealignment, a decrease in the importance of partisanship itself.

From 1952 to 1984, the percentage of white southerners who identified themselves as independents has tripled, from 13 percent to 39 percent; in 1984 self-described independents outnumbered both self-described Democrats and Republicans among white southerners, according to the University of Michigan Center for Political Studies. And in every presidential election since 1952, southerners have split their ticket more frequently than the nation as a whole.

Over the same period, black southerners have become more monolithically Democratic, both in registration and in voting habits.

The decline in the importance of political parties was on everyday display here in North Carolina during the just-completed primary campaign. Thousands of political billboards and yard signs dotted the streets and highways -- but candidates advertising themselves by party were a rarity. "I don't remember seeing a one," said Robert Shaw, a former GOP state chair from Greensboro. "Times change."

Even dealignment, of course, is a net gain for the Republicans. If Democratic candidates don't feel safe advertising their party affiliation in a state where Democratic voters still outregister Republicans by 2.6 to 1, their party has lost something of value.

The question now is how much Republicans can capitalize on their opportunities. Can they become a fully competitive, perhaps even a dominant, grass-roots party here?

Intraregional distinctions are necessary. The Republicans' greatest hopes are in the growth areas. "Follow the interstates and that's where you'll find us," said South Carolina GOP executive director Warren Tompkins. "Our best prospects are where there is a television station, where people are moving in and where there's growth," said Jay Morgan, director of the Georgia GOP. "It's not like Mississippi, where they have to go back and try to convert the same people each year. We don't have to convert that many."

Since 1956, 49 percent of all white migrants to the South have been Republican, roughly double the percentage of native whites, according to political scientists Ray Wolfinger and Michael C. Hagen. And as recently as 1976, 44 percent of all white southern Republicans were transplanted Yankees. In the past decade, however, as native southern fundamentalists have changed their affiliation, that percentage has dropped.

Over the past two generations, migratory patterns have been a double plus for the GOP. Blacks have been moving out, and now constitute 20 percent of the region's population, down from 25 percent 30 years ago. (In the past 10 years, there has been a reversal: a small net immigration of blacks.)

And whites, of course, have been moving in. Consider the partisan impact of migration on the region's two greatest-growing states. In Florida, Republicans have added 484,000 new registered voters to their rolls since 1980, compared to the Democrats' 33,000. In Texas, more than half a million people voted in this months's GOP primary -- more than triple the number who voted in the GOP primary when Clements first ran, in 1978.

By the same token, slightly over 1 million voted in the Democratic primary this year, about 60 percent of the number who voted in 1978. "Every vote in a GOP primary is like two votes -- one cast for a Republican, and one not cast for a conservative Democrat," noted Marty Connors, Alabama GOP executive director. (The analysis goes as follows: As the Republicans siphon off conservative Democrats in primaries, the Democratic Party becomes more likely to nominate liberal or black candidates, who have a hard time winning general elections).

Growth is not the only formula for GOP gains. In Louisiana between 1984 and 1986, the size of the GOP delegation in the state legislature increased from 10 to 25 -- without benefit of an election. All the growth came from elected officials who switched parties after state and national GOP operatives showed them detailed voting and demographic charts of their districts; promised them money to make constituent mailings to explain their change; and, at least implicitly, threaten them with GOP opponents if they did not switch.

The "switcher" program has been less successful elsewhere in the South, where Republicans did not reach self-imposed quotas for converting Democrats voters. And the record of "switchers" as candidates is mixed at best.

In 1985, the biggest GOP trophy in the South was former House member Kent R. Hance (Tex.), who became a Republican after narrowly losing a Democratic Senate primary in 1984. This year Hance finished a distant third in the GOP gubernatorial primary. A setback for the GOP outreach program? Yes, but there is a silver lining, too. "The Republican won that one either way. If it worked out for Hance as a Republican, fine," said one Texas Democratic strategist. " If not, well, they've destroyed the career of an attractive conservative Democrat."

In addition to growth and switching, a third factor has boosted GOP grass-root strength in the region--technological sophistication.

In Tallahassee, the Florida GOP has a high-technology headquarters with printing presses, a photography lab, a phone bank, and computers containing the names, addresses, phone numbers and voting records of 3.1 million voters. Sixty part-time paid workers operate the phone banks 12 hours a day. The party has an annual budget of $4.3 million, more than double that of the Democrats. Last year, when the staff of the state GOP challenged the state Democrats to a softball game, it never came off. The GOP had a full roster of 23; the Democrats could not field a team with their staff of seven. (Again, the GOP advantages are not uniform throughout the South. In Arkansas, the state GOP has no paid staff, no photocopy machine, no credit cards, and it works out of a cramped office above the Little Rock bus station.)

One final factor that has favored Republicans: Voting rights cases. In 1982, the state GOP and NAACP filed suit against the multimember district system used in North Carolina's legislative elections. When they won, lines were redrawn that created secure black districts and competitive Republicans -- leaving white Democrats bleeding on both sides. "Used to be with multimember districts , every Republican candidate in Greensboro would start out 16,000 votes behind the minute the polls opened," said Robert Shaw, the former GOP state chair elected to the legislature from Greensboro in 1984. That is his way of counting the cost of running in a multimember district that includes black precincts. "Now, we're free of that," he said. Nearly half the 24 state legislative seat pickups for the GOP in North Carolina came in districts where lines had been redrawn this way -- and the pattern repeats itself in several southern states.

For Democrats, of course, blacks are both the core of strength at the local level and the core of weakness: They continue to be 90-plus percent loyal, but their heightened profile within the party has helped drive whites away.

Can the Democratic Party be successful over the long haul as a biracial coalition? The challenge is every bit as daunting as the Republican dilemma of keeping fundamentlists and economic elites within the same party. NEXT: Race and southern politics. Reporting and research for this series was provided by staff writers David S. Broder, Milton Coleman, Thomas B. Edsall, David Maraniss, Bill Peterson, Tom Sherwood and Paul Taylor and staff researcher Michael S. Slevin.