The dozen men who would be president share two hours of live prime-time television tonight at 9 in a novel format that will offer alternating half-hour dollops of the six Democrats and six Republicans.

The NBC-sponsored debate marks the network television debut of the 1988 presidential campaign -- and the first and only time all twelve are scheduled to appear as an ensemble.

"This is Broadway," said Democratic media consultant Robert Squier. "This is 'Are you ready for prime time?' These men are going to be talking to the people who will decide their careers. There are no opening or closing statements, which takes the staffs and the consultants off the stage. This is just the candidates, out there on their own. It's a big deal -- the first electric primary."

Not everyone shares Squier's high hopes for the evening, however -- in part because almost no one can figure out how the complexity of the format will affect viewer interest.

"It's a bipartisan cattle show gone amok," said David Keene, a political consultant to Senate Minority Leader Robert J. Dole (R-Kan.), "and a damn fool idea -- designed more to feed the egos of the producers than to shed light on anything."

"The impact is likely to be minimal, because there will just be too much on the air for anyone to absorb," concurred Republican media consultant John Deardourff. "People are waiting for the process to sort itself out before they get involved. I suspect the ratings will drop off quickly after the first few minutes."

NBC projects the initial audience at up to 25 million.

The format calls for four half-hour segments: Democrats on foreign policy, followed by Republicans on foreign policy, Democrats on domestic policy, and Republicans on domestic policy. The Democrats go first because Republican National Committee Chairman Frank J. Fahrenkopf Jr. won a coin toss and elected that his team bat cleanup.

Within each segment, NBC anchorman Tom Brokaw will question all six candidates, then each will question a rival chosen by lot. NBC had originally envisioned a free-for-all in which candidates could debate across party lines, but that idea was dropped when several GOP campaigns objected.

The show will be staged at the Kennedy Center before an audience of 1,000. While one party's six-pack has its turn on the air, the other party's hopefuls will observe from on-stage bleachers.

The debate is the last major event of the longest campaign pre-season ever. Voter interest, which seems to have been minimal throughout, is expected to intensify around the first of the year. The first caucuses will be held on Feb. 8 in Iowa.

Even though most of the Democrats remain little-known, tonight's debate marks the 11th time -- a record -- that they have all appeared together in a debate. It is only the second time for the Republicans. Some Democrats have already complained of "debate fatigue" and "debate staleness," but informal efforts to limit joint appearances have so far been unavailing. Roughly a dozen more Democratic debates and a half-dozen Republican debates are expected in the first three months of next year.

With Soviet leader Mikhail Gorbachev scheduled to arrive here next week, the intermediate-range nuclear forces (INF) treaty that he and President Reagan will sign is certain to be a major topic tonight. All six Democrats endorse the treaty, but fireworks are likely on the Republican side, where only Vice President Bush is supporting it. The others are either unequivocably opposed or have expressed concern about verification provisions, past Soviet treaty violations and conventional force imbalance in Europe.

Bush's strategists argue that the issue is a godsend for him. A new NBC poll, for example, shows that 77 percent of likely caucus-goers questioned in Iowa and 74 percent of likely GOP voters in New Hampshire favor the treaty. While Bush's rivals make a play for the party's hard right wing, Bush strategists said, he can appear as a man of peace. Several observers said the hot seat on the issue tonight could be occupied by Dole.

"Dole has got to take a position on the INF," said GOP pollster Linda Divall. "He can't continue to say, 'I haven't read it yet.' And to the extent that {Rep. Jack} Kemp, {former Delaware governor Pierre S. (Pete)} du Pont and {Marion G. (Pat)} Robertson pressure him from the right, he could wind up as the man in the middle."

Although Dole was criticized for a lackluster performance in the first GOP debate, the latest NBC poll gives him the lead over Bush in Iowa by 42 to 26 percent in a survey of 815 likely Republican caucus-goers. The other Republicans are far behind. In New Hampshire, Bush holds a 20-point margin over Dole among 1,145 likely GOP voters questioned there.

On the Democratic side, the candidate thought most likely to be a lightning rod for attack tonight is Sen. Paul Simon (D-Ill.), who edges out Massachusetts Gov. Michael S. Dukakis in NBC's poll of 890 likely Democratic caucus-goers in Iowa. The poll has Simon at 21 percent; Dukakis at 20 percent; Rep. Richard A. Gephardt (Mo.), 10 percent; Jesse L. Jackson, 9 percent; former Arizona governor Bruce Babbitt, 3 percent, and Sen. Albert Gore Jr. (D-Tenn.) at one percent, with 33 percent undecided.

Simon has recently come under attack for his "Simonomics" -- his proposals to launch expensive social programs and balance the budget within three years without expecting to have to raise taxes.

"Once we moved out front, we figured we'd become a target," said Simon press secretary Terry Michael. "We won't back off. We'll forcefully state our message, which is the use of the activist tool of government, within the context of a balanced budget, by a man you can trust."

While Simon readies for an attack, it probably won't come from the Democratic front-runner in New Hampshire, Dukakis, who had 49 percent there in the NBC poll while Simon was a distant second at 13 percent, with 23 percent undecided. "We don't feel a strategic imperative to make progress by going after other candidates," said Dukakis' communciations director, Leslie Dach.

Given that this will be the first mass audience of the campaign, and that the divided format discourages lengthy exchanges, it seems likely that most candidates will take a similar play-it-safe-and-straight strategy into the debate.

But put 12 healthy egos on stage before millions of viewers, and almost anything can happen. And, in the view of some, it ought to. "It's later than some of these fellows think," said Robert Beckel, 1984 campaign manager for Walter F. Mondale, "and the time for hitting singles is over. Some of them need to go for the fences."