When Americans tune in to tonight's presidential debate, they will be treated to a discussion of big issues: Medicare, the environment, taxes.

But for months, advisers to Al Gore '69 and George W. Bush have been haggling over the little details, the kind many voters may not consciously notice--like the height of lecterns, or who gets to speak for how long, even the size of the candidates' greenrooms.

Their intensive preparations reflect the fact that presidential debates can turn on the most minor mishaps. And both sides have been jockeying for the slightest possible advantages.

According to the format worked out by the two campaigns and the independent Commission on Presidential Debates, each debate will last for 90 minutes and be presided over by NewsHour's Jim Lehrer, who brings moderating experience from three previous presidential debates. Lehrer has also been given leeway to create questions himself.

Both of the major candidates and their campaign representatives have had ample opportunity to fight over the more mundane, seemingly arbitrary aspects of the event, said John Scardino, a spokesperson for the commission.

There is "a fairly detailed list of issues the candidates and their representatives get involved in," Scardino said. He attributed this concern for detail to the conventional wisdom that the widely-viewed debates will have a significant impact on November's election results.

Of course, the campaigns have every reason to be concerned; as much as the public and press lament the carefully-scripted flavor of American politics, they have been historically unforgiving of campaign-season gaffes.

In 1988, Michael Dukakis's mechanical reply to a debate question about how he would react to his wife's rape and murder crystallized his reputation as an automaton.