ATLANTA, FEB. 13 -- A political wrecking ball is poised to swing through the fragile walls of the southern Republican Party, and Marguerite Williams, who first got into GOP politics during Wendell Willkie's 1940 presidential bid, is standing right in its path.

Williams is the kind of loyalist who helped form the elite core of the southern GOP. Wealthy and civic-minded, she is a national trustee of a historic preservation group. She donated a desk once owned by Thomas Jefferson for use in the Adams Room, where the State Department holds diplomatic functions.

After years of working up from precinct captain, she is now in her first term as a Georgia Republican national committeewoman, and she would like to serve longer. In any normal presidential election year, she would be a sure delegate to the Republican National Convention.

Her prospects for reelection, however, have taken a nose dive in the last 10 days. The Georgia Republican Party's machinery is being taken over by the army of evangelical Christians backing presidential candidate Pat Robertson, and the troops are taking no prisoners.

"I hope I am acceptable to them," Williams said. "I would hope decisions are made fairly."

Brant Frost IV, Robertson's Georgia state director, said there is little chance that any party posts will be conceded to those who are not Robertson partisans.

"Reagan beat Mondale 60-40. He didn't give Mondale 40 percent of the Cabinet," Frost said. "The 'God, family and country' people are out there by the millions. I feel like I'm on a surfboard riding a tidal wave . . . . The Republican Party is the vehicle."

The Robertson campaign here and elsewhere has developed an innovative and aggressive strategy to use battles for control of local parties as a vehicle to control selection of delegates to the national convention, no matter who wins the primary elections.

This tactic -- which appears guaranteed to succeed here and is likely to pan out in North Carolina, Mississippi, Virginia and to a lesser extent in at least four other southern states -- could prove critical in a deadlocked convention.

In a deadlock, the outcome could turn on a key procedural or rules vote on the convention floor, when the Robertson loyalists would be free to cast their ballots in any way they choose, even if required to vote for a particular candidate in direct votes to nominate a candidate.

Georgia offers perhaps the best example of Robertson's strategy.

While most presidential campaigns are geared to the relatively simple task of winning pluralities and majorities in primaries and caucuses, Robertson's long-range strategy is clearly to build a power base through the party's local structure. These drives not only build Robertson's troop morale with precinct and county victories, but also provide the mechanism to name national convention delegates in such states as Georgia, North Carolina and Mississippi.

In Georgia, officials say they expect the overwhelming majority of delegates, if not all of them, to be Robertson loyalists, no matter who wins the primary March 8. Robertson forces began taking over the state party in precinct caucuses in the 10 largest counties earlier this month, and they are expected to complete the job later this month when all counties hold meetings. In the preliminary test of a similar struggle in North Carolina, the Robertson forces have crushed the establishment in the state's largest county, Mecklenburg.

These maneuvers suggest that power within the southern GOP is shifting toward the Christian right, and that Robertson may well have significant bargaining power at the national convention in New Orleans if the nomination fight continues till then.

If, for example, Vice President Bush wins a majority in Georgia, most of the delegates will be bound to vote for him on the first and second ballots of the convention. But they will not be required to vote on Bush's side in procedural tests, which can set the tone in a fight for the nomination. At the 1976 GOP convention, the key vote was on a motion to require President Gerald R. Ford to pick a vice president in advance of nomination, a motion that failed and set the stage for Ford's defeat of Ronald Reagan.

The Robertson forces are also clearly committed to party takeover moves in states where there will be no direct benefit to Robertson's campaign. This commitment suggests that Robertson and his strategists are in the fight for the long haul, intent on achieving goals beyond the presidential fight. "It's not a short-term deal," Frost said.

"I will sit here as party chairman and tell you that there is a lot going on out there I don't know about," Texas GOP head George Strake said in an interview.

In Texas, Robertson partisans not only are preparing to cast their ballots March 8 for the former television minister, but are passing out detailed instructions for going to precinct caucuses that night to elect local representatives to the state GOP.