The format, as we have been told, precludes any genuine give-and-take between the presidential candidates. It is not so much a debate as it is a simultaneous press conference, with rebuttals. Yet the reality remains: since 1960, televised presidential debates have three times profoundly influenced the American electorate's choice of a national leader.

In 1960 John Kennedy, disparaged as callow and inexperienced, cancelled both charges in his first debate with Richard Nixon.

Sixteen years later, in the next presidential campaign in which the candidates debated, incumbent Gerald Ford interrupted his own valiant comeback -- from a 20 million vote deficit to a virtual dead heat -- by "liberating" Poland in that year's second debate in San Francisco.

In the 1980 campaign's only debate between the major party nominees, Ronald Reagan was not, as his critics had predicted he would be, exposed as either a fraud or a risk. Instead, by being avuncular and reasonable and by not advocating a personal nuclear device for every ROTC graduate, Reagan erased the mad-bomber image.

The impressions voters take of the candidates from the televised debates frequently last. In 1960, after watching the candidates debate on television, Marshall McLuhan saw Kennedy with the image of a "shy, young sheriff" and Nixon resembling "the railway lawyer who signs leases that are not in the best interest of the folks in the little town." It's a good bet that the 1984 debates will influence the outcome of the 1984 election, too.

The background: Ronald Reagan is to be commended for debating. In 1964 and 1972, presidents Lyndon Johnson and Richard Nixon -- incumbents with big leads in the polls -- both ducked debates with their underdog opponents.

In late 1979, after the takeover of the embassy in Tehran had transformed him from "weak" Jimmy to "strong" Jimmy and raised his poll numbers by close to 40 points, President Carter pulled out of the Des Moines Register debate with Edward Kennedy and Jerry Brown before the Iowa caucuses.

By agreeing to debate, Reagan is providing his underdog challenger, Walter Mondale, with the largest crowd -- maybe 120 million -- ever to see and hear him. At the same time, Reagan is probably guaranteeing that his Oval Office successors will never again be able to duck a debate challenge from their opponents without looking like large chickens.

Mondale's chance: The challenger has a number of real advantages. For the first time in his own remarkable political career, Ronald Reagan may be overrated going into a showdown. In 1966 Pat Brown, the Democratic incumbent governor of California, had wished for Ronald Reagan to run against. Brown gothis wish, and Reagan won by a million votes. In 1980 the Carter campaign lived in dread of the Republicans' nominating for president the eminently electable Howard Baker or the respectable George Bush. If only, Democrats hoped, the collective Republican death wish would nominate Ronald Reagan, the conservative ideologue and former Boraxo pitchman.

But after four years of being told what a gifted communicator the president is, few of us hardly expect Mondale to get so much as a first down. This is an advantage for the challenger, who is quick on his feet and bright.

Mondale must remember: Americans do not like pedants in their car pools or in the Oval Office. Mondale cannot be a showoff, telling us how much he knows. Mondale cannot do what Sen. Joe Biden did to William Clark at Clark's confirmation hearings to be undersecretary of state. That was when Biden embarrassed Clark by asking him a string of questions about foreign affirs that sounded like something out of an international trivia game, including just about everything but "What's the national anthem of Chad?" and "What are the principal products of Liechtenstein?"

People are kind, and recoil at that sort of treatment. If Mondale tries to expose the president's alleged lack of knowledge, he must do so on a)something the president says Sunday night (not something he said in 1981) and b)something most of us know.

Debates are "wholesale" events. No longer can either candidate seek to tailor his message to a specific group of either steel workers or parents with children in parochial schools and tuition tax credits on their mind. Fritz Mondale will speak, courtesy of Ronald Reagan, to the most Republicans and independents who will ever hear him. At least until his inaugural.

Whatever else Mondale does on Sunday, he must speak to all of us at the same time, not as members of a professional or demographic group, but as Americans with an interest in our own and the nation's future.