Atlanta — This is an important week for the Democrats. It is the week when it may become clear whether Geraldine Ferraro can stir up more enthusiasm and support for Walter Mondale in the South. The Democratic presidential candidate must win at least one or two big states in the region to have a chance in November, according to key Democratic campaign officials.
The two candidates make campaign stops together this week in Mississippi, where they are counting on a strong black turnout in the election, and in Texas. But clearly Texas and Florida, the states with the most electoral votes in the region, are the keys to Democrats' Southern strategy.
''We have to win somewhere in the South,'' says Bert Lance, general chairman of Mr. Mondale's national campaign. And he names Texas and Florida as key targets.
In Texas, the man who is likely to be named the Mondale-Ferraro state campaign chairman, Duane Holman, says: ''I haven't come up with an electoral scenario yet that lets Fritz (Mondale) win without Texas.''
As of now President Reagan appears to be ahead in both Florida and Texas, according to a number of Democratic Party activists and officials in those states.
There is no good measure yet of whether or not Ms. Ferraro's presence on the ticket could turn away more Southern voters than it attracts, or if it will make much difference. But scattered response so far from Democratic Party activists and other sources in Florida and Texas is mostly positive.
''She's lit a fire under all the women,'' says Mayre Lutha Tillman, immediate past president of the Democratic Women's Club of Florida.
Sending ''just Ferraro'' into Florida would be fine, says Michael Shea, a former Democratic National Committee member from Florida.
In Texas, some Democrats make similar remarks. But in both states Democrats see a tough race ahead.
''The response about Geraldine Ferraro has been one of great enthusiasm'' in the South, says Mr. Lance. She will definitely help in Florida, he said in a telephone interview from his home base in Calhoun, Ga. He calls Texas a real ''contest.''
''I don't know of anywhere we're sure to win - or lose,'' he says, but adds: ''If you can win in Texas you can win in other Southern states.''
New arrivals in fast-growing Texas are ''definitely making it more Republican ,'' says David Hill, a political scientist at Texas A & M University. Republican Party affiliation in the state has grown from 8 percent in 1964 to about 26 percent today. During the same time, Democratic affiliation has decreased from 65 to 37 percent, says Mr. Hill, who is also director of the Texas Poll.
A key group in Texas are the independents - about 1 out of every 3 voters. And about two-thirds of them are Republican ''leaners'' who often vote for a Republican president, Hill says. President Nixon in 1972 and Ronald Reagan in 1980 both easily carried the state. Jimmy Carter's 1976 victory was much closer.
''I don't think Reagan is very far ahead in Texas,'' says Robert Slagle, chairman of the state Democratic Party. ''I think we're gaining,'' he says. Ms. Ferraro is making a difference, he adds.
''We want her in our state early and often,'' he says. Her experience as a prosecutor, prior to her election to Congress, will be ''a big asset in our state,'' he adds.
''Mondale was in a lot better in this state a year ago than he is now,'' Mr. Slagle says. The ''pounding'' the former vice-president took during the primaries hurt him, he explained.
Slagle looks to Democratic voter registration efforts among blacks and Hispanics to make the difference in an expected tight race. Since 1980, he says, about 100,000 blacks and more than 400,000 Hispanics have been signed up.
Juan Maldonado, chairman of the Mexican-American Democrats of Texas says south Texas will be ''solid'' for Mondale, and that Ms. Ferraro is a plus.
But Republicans are also signing up voters favorable to them. And Mr. Hill calls the Hispanic vote in Texas ''unpredictable.''
In Florida, the Miami-area Cuban vote is strongly for Reagan, according to Republican and Democratic Party officials. Statewide, the Cuban community may account for less than 2 percent of the vote, but in a tight election that could be important, says Alfredo Duran of Miami, former state party chairman.
As in Texas, most Florida Democratic Party officials contacted are excited about Ferraro and say she is already helping the ticket. She is ''clearly an asset in south Florida,'' says Mike Abrams, who ran the Gary Hart primary campaign there.
Mondale's support among Jewish voters in south Florida is ''deep,'' he says, but as to where the Hart supporters will end up, ''the jury is still out on that.'' They could go to Reagan, he says.
Some tradition-oriented Southern women may balk at the presence of Ms. Ferraro on the ticket, says Mr. Shea. But he notes an increase in the number of women being elected to office in Florida.
Hazel Evans, an active Democrat in St. Petersburg, says having Ms. Ferraro on the ticket is ''going to hurt him (Mondale) tremendously.'' Some elderly Democratic women she has spoken with since the convention are opposed to a woman being on the ticket, she adds, but they may simply not vote.