DES MOINES, JAN. 14 -- "Bruce Babbitt could stand up and take his pants off. The story of this debate is still going to be Gary Hart."

With equal measures of amusement and exasperation, Chris Hamel, Babbitt's Iowa campaign manager, was grappling with a question that's on the mind of Democratic tacticians as they prepare for a debate here Friday night that marks former senator Hart's debut on stage with his six rivals for the presidential nomination.

How will the others deal with the return of the prodigal candidate -- this political curiosity who, according to the polls, is both the most popular and most unpopular figure in the Democratic field? Will they go right at the issues that drove him out of the race last spring? Will they ignore them -- at the risk of leaving the impression they don't matter? Or will they try to engage Hart on some other front?

Strategists for the other campaigns freely confess to still being off-balance a month after Hart's return, but the consensus seems to be to lay off the Donna Rice episode.

"It's just too risky; it's too hard to raise it without losing ground yourself," said one top adviser to another Democrat, arguing that raising the issue could create sympathy for Hart.

Earlier this week, former Arizona governor Babbitt discovered, without intending to, just how close to the surface the whole matter is. During a debate in Sioux City with three other Democrats, he posed a fiscal question to the absent Hart. "Gary Hart isn't here," Babbitt began. "I don't know where he is tonight, but . . . . " The remark was worded in all innocence, his advisers said, but many in the audiences began to snicker, perhaps thinking that they had been treated to a double-entendre.

Some advisers said they are contemplating having Hart confronted with the issue of his $1.1 million debt from his 1984 campaign. "You can use that as a metaphor for character, for questioning whether this is a guy who keeps his commitments or walks away from them," the strategist added.

Of all the candidates, Babbitt is considered the likeliest to take Hart on; in part because it could help him gain some desperately needed momentum. The irony here is that recently Hart has credited Babbitt for forthrightness on what the former governor sees as the need to raise federal revenues to balance the budget. But Babbitt is expected to challenge Hart on revenue measures they differ over, such as Hart's support for an oil import fee.

Others campaigns are less concerned about Hart. The debate would be a critical two hours for them even without the complication of his return, for it is the one event of the Iowa campaign that will be watched by as many as half the Democrats who will attend the Feb. 8 caucuses. (It is being televised live in Iowa and from 7 to 9 p.m. Friday in the Washington, D.C., area on WETA).

It comes when, although Sen. Paul Simon (D-Ill.) is the widely acknowledged Iowa front-runner, there is a persistent sense that the contest is still wide open. Any of four candidates -- Simon, Massachusetts Gov. Michael S. Dukakis, Rep. Richard A. Gephardt and even Babbitt -- have good enough organizations in place that if they were to strike a match with the voters, they could become formidable overnight. The same is not true of Jesse L. Jackson and Sen. Albert Gore Jr. (D-Tenn.).

"Throw out everything that has happened so far," said Democratic pollster Peter Hart, who is not working for any candidate and is a leading proponent of the surge theory of this campaign. "If anyone has two good weeks starting on Friday night, that's the person who wins the state."

The Des Moines Register debate has a history of kindling fires. Four years ago, former senator George McGovern used it to make his call to "vote your conscience" and wound up finishing a respectable third.

Hart, who has few aides, will try to do something similar -- challenging his supporters that it is their civic duty to find the caucus sites without help from paid political hands. Hart came in second in Iowa in 1984.

But the candidate who seems best positioned to catch a surge out of this debate is Gephardt. Of everyone in the race, he is spending the most on advertising this month, and his tub-thumping oratory -- both in his ads and in person -- has moved his support in the polls back into the double digits. Most Democrats staffers here think he has pulled even with Dukakis, behind Simon.