JACKSONVILLE, FLA. -- When Rep. Richard A. Gephardt swung through here the other day for a fund-raising luncheon, he impressed a young local dentist as having ''the kind of charisma my parents said John Kennedy had.'' But, he added, ''Gephardt could walk out on the street here and not a soul would know him.''
That comment capsulizes the most serious problem the Democrats face going into the 1988 presidential election. It also illuminates the party's continuing preoccupation with the noncandidacy of New York Gov. Mario M. Cuomo.
A swing through North Carolina and Florida, two of the key states in the South, suggests that none of the Democratic candidates except Jesse Jackson has penetrated the consciousness or enlisted the enthusiasm of many voters 3 1/2 months before the March 8 Super Tuesday primaries in this region.
A traveling reporter is asked constantly about Cuomo's intentions, not because voters necessarily want to support him but because something about his personality has caught people's attention. A widespread feeling exists that Gephardt and his four equally unknown white rivals cannot plausibly be thought to exhaust the Democrats' resources for the White House contest.
The indifference of southern white voters to the active Democratic contenders is potentially crippling. History shows Americans are extremely reluctant to put a stranger in the White House. Only once since Franklin D. Roosevelt's death has the nation picked a president who was not widely known at least a year before Election Day. People understand that the occupant of that job will make decisions that will affect them and their children, their communities, their country and the world. They are justifiably cautious about entrusting that power to an unknown.
The lone exception was Jimmy Carter, as little known a year before his election in 1976 as Gephardt, Michael Dukakis, Bruce Babbitt, Albert Gore Jr. and Paul Simon are today. And Carter has become a kind of cautionary tale to many voters -- a reminder of what can happen when people pick a president on brief acquaintance.
Yet Carter is another kind of example to the Democrats. He is the only winner they have chosen in the past five elections and, not coincidentally, the only southerner nominated in that span of time.
For that reason, the inclination to look south for the nominee was strong among Democrats when this election cycle began. And the fact that they now find themselves with nothing but a pair of border state aspirants in Missouri's Gephardt and Tennessee's Gore is part of the frustration southern Democrats freely express about the 1988 race.
A chart in a recent edition of the National Journal demonstrates the soundness of that Democratic apprehension. Its six-color coding dramatically illustrates the concept of the ''electoral college lock'' introduced into political analysis by Washington consultant Horace Busby years ago.
In vivid hues, the map shows the broad band of states across the South, through the Middle West, the Mountain states and the Pacific Coast, which Democrats have carried three times or less in the past seven elections. Computing the quadrennial Democratic vote percentage between 1960 and 1984, National Journal shows there are only seven states and the District of Columbia, with 76 electoral votes, where Democrats have averaged more than 50 percent.
''If the Democratic presidential nominee next year were to win those states and all of the states in which they averaged from 47.51 to 50 percent of the vote since 1960,'' National Journal reports, ''they would increase their electoral vote total only to 154.'' That would leave the Democrats still well short of the 270 electoral votes needed to win the White House.
To break the Republican ''lock,'' Democrats need a candidate who can move well beyond that base -- who can convert Republican presidential voters from the pattern of the past. The Democratic Leadership Council, a southern-dominated group of party moderates, presented evidence last month that Gore or Gephardt might eventually be able to do that.
It paid some 300 people in Jacksonville, Atlanta and Charlotte to watch a televised debate among the Democratic candidates. All of the voters had backed Reagan in 1984 and a Democratic Senate candidate in 1986. After watching the debate, they had substantially more favorable impressions of Gore and Gephardt, but only 38 percent of these ''swing'' voters were ready to support Gore for president, and only 19 percent had similar confidence in Gephardt.
That is far from a breakthrough. It suggests why there is such a hankering for somebody else -- somebody with the magic that is missing from the current field. On paper, Cuomo looks like the last person who could solve the Democrats' dilemma in the south. But so long as the other candidates can walk out on the streets of Jacksonville or Raleigh or Atlanta or Austin unrecognized, Democrats will continue to look longingly elsewhere.