MANCHESTER, N.H. -- The operative question about the Steve Forbes phenomenon is supposed to be this one:
Does the millionaire publisher have the potential to be a serious candidate for the Republican presidential nomination or only to make a little trouble for Senate Majority Leader Bob Dole?
The answer may be something in between -- that Mr. Forbes will end up making serious trouble for Senator Dole without becoming a genuine contender himself. And that, in turn, could mean a contest for the Republican nomination far more open than it appears to be with less than a month to go before the New Hampshire primary.
At this stage, Mr. Dole's lead in opinion polls here seems imposing enough. Three recent surveys have shown him with 30 37 percent among likely voters in the February 20 primary.
Mr. Forbes runs second with 17 to 21 percent and clear daylight between him and the also-rans -- commentator Patrick J. Buchanan, Sen. Phil Gramm of Texas and former Gov. Lamar Alexander of Tennessee.
But for Dole partisans the trend is unsettling. Support for the Senate leader was running 50 percent or better last fall, and none of the others had shown any ability to break away from the pack as Mr. Forbes now has done.
Moreover, the surveys here are showing a steady rise in Senator Dole's negatives, an unsurprising result of the fact that Mr. Forbes has spent most of his $10 to $12 million outlay so far on television commercials attacking him as the quintessential ''Washington politician.''
The Dole campaign obviously takes the attacks seriously. It has been running commercials of its own here accusing Mr. Forbes of advancing ''risky ideas,'' charging that his signature proposal for a 17 percent flat tax would add $186 billion a year to the federal deficit.
''The more you learn about Steve Forbes, the more questions you have,'' the Dole commercial warns.
Messrs. Gramm and Alexander, the two conventional candidates who had been expected to be Senator Dole's chief rivals, also are finding it necessary to cut down Mr. Forbes if they are going to have any shot at the leader. Thus, Mr. Alexander derides the flat tax as a ''nutty idea'' that would wreck the economy, and Senator Gramm depicts Mr. Forbes as a nuisance candidate on whom primary voters would be wasting their ballots.
Not a plausible candidate
''I don't find anyone who believes that Steve Forbes is a plausible candidate for president,'' Mr. Gramm said the other day. ''Does anyone really believe that Steve Forbes would beat Bill Clinton?''
The obvious problem with these attacks on Mr. Forbes by all three of the putatively ''serious'' candidates in the field is that they add to his stature. If he is so trivial, why are they spending so much of their time and treasure trashing him?
In fact, Senator Gramm is correct in his assessment, to the degree it is limited to conventional politicians. It is hard to imagine the circumstances under which a 48-year-old political neophyte, even one with a $400 million personal fortune at his disposal, captures the nomination.
But Mr. Forbes' advertising campaign already has exposed some softness in the support for Senator Dole, as the poll figures here demonstrate.
And there may be a streak of contrarianism in the electorate this year as there was in 1992, when one-fifth of the voters ended up casting their ballots for Ross Perot even after he had shown he was temperamentally ill-equipped for the White House.
Senator Dole's greatest strength, his long record, is also his greatest liability with those voters anxious to repudiate ''Washington politicians.''
The danger for Senator Dole is that Mr. Forbes will do enough damage to his image to cut his winning margin in the Iowa caucuses below expectations and thus invite primary voters here to take a fresh look at the whole question of whether a Dole nomination is inevitable.
If, for example, Mr. Dole were to win in Iowa with less than 30 percent of the vote, a Gramm or Alexander with, let's say, 18 to 22 percent, might be considered formidable.
The most likely prospect is that the Forbes meteor will fizzle out as he comes under closer scrutiny and his organization is put to the test in Iowa. But right now nobody knows.
Jack W. Germond and Jules Witcover report from The Sun's Washington bureau.