Atlanta — The crowd outside Walter Mondale's campaign headquarters here extended out into the street. Balloons were taped onto the outside of the small building. An outside speaker was not connected, so few people on the street could hear Mr. Mondale inside as he addressed campaign workers. But that didn't seem to bother the mostly suit-and-tie crowd that stood chatting among themselves on an unusually warm winter afternoon recently.
But when this writer approached a black man in the crowd to ask why he supported Mondale, he said:
''Promise not to use my name and I'll whisper something to you.''
What he whispered was: ''I'm for (Jesse) Jackson.'' A second black man, active in the Democratic Party here, also said he was for Mr. Jackson.
Jackson supporters at a Mondale rally?
It illustrates how blacks here feel pulled in two directions in the presidential campaign.
On the one hand, many of them like the Rev. Mr. Jackson. They respect his long struggle for civil rights and are proud to see him taking on the establishment presidential contenders in what, by most standards, is an unorthodox campaign.
But if there is any unanimity in the black community here - from Mayor Andrew Young down to 18-year-old Jared Samples - it is on the aim of defeating a reelection bid by President Reagan.
And Walter Mondale is seen as the ''best chance'' of doing this, says Robert Brisbane, a black political-science professor here.
Birmingham's black mayor, Richard Arrington, recently addressed this same dilemma when he endorsed Mr. Mondale for president, during Mondale's recent five-day, five-state swing through the South. But Mayor Arrington also endorsed Mr. Jackson for vice-president, as the state black Democratic organization had in December.
When blacks enter the voting booths March 13, as Florida, Alabama, and Georgia hold their presidential primaries, ''they're going to be torn'' between Jackson and Mondale, says a black minister here. Asking that his name not be used, he said he basically supports Mondale but also supports the Jackson ''candidacy'' for its potential in attracting more blacks to be voters.
But, he added, there is a risk that many black voters will feel so ''let down'' by a Jackson defeat race they will again turn away from voting, and thus set back black political progress.
Atlanta Mayor Andrew Young is staying neutral, although he is assumed among blacks interviewed here to be a Mondale supporter. The mayor is looking beyond the nomination to the need to pull all Democrats behind their party's nominee to defeat President Reagan, a spokesman says.
Georgia State Sen. Julian Bond, a black, has endorsed Mondale. Former Atlanta Mayor Maynard Jackson has endorsed Jackson as ''a man of true grit.''
The Darden poll of the South among registered Democrats showed Jackson with about 9 percent support, all but 15 percent of which was black. (The margin for error was high because of the small number of persons who said they were Jackson backers.) A more recent poll, not yet released, shows about the same level of Jackson support. Mondale got 43 percent and Sen. John Glenn 29 percent in the November poll.
Jackson's recent trip to Syria, where he obtained the release of the sole American POW, is generally praised among blacks interviewed. But Michael Lomax, a black leader in county government here and an early supporter of Gary Hart, questions whether Jackson let himself become a ''pawn'' of the Syrian government.
But, he said, however they vote, ''blacks are going to the poll and vote against Reagan.''
So far there is no Jackson campaign office or director in Atlanta, although several statewide roles have been filled. ''It's hard when you don't have much money,'' says state Rep. Tyrone Brooks, Georgia coordinator for Jackson.