SIX MONTHS ago, when Paul Simon entered the presidential race, the prevailing wisdom among political pundits was that the 58-year-old, first-term Illinois Senator's horn-rimmed glasses, massive earlobes, and trademark bow tie made him unelectable. His unabashed New Deal liberalism wouldn't sell in these budget-cutting times, everyone was sure.

Now, however, recent polls show Simon with an impressive lead over the rest of the Democratic field in Iowa and trailing only favorite-stepson Michael Dukakis in New Hampshire.

In a year in which the ubiquitous "character issue" has taken on as much importance as positions on arms control and the deficit, Simon has made good use of his off-beat image, which he advances as evidence of authenticity and personal integrity. After the scandals on Wall Street and in the White House, many voters, especially the legions of Democrats who now rue the day they voted for Reagan, are looking not for the most attractive and articulate candidate but rather for the candidate whom they perceive as the most trustworthy, the most genuine. That's where Paul Simon comes in, or would like you to think he does.

"If you want a slick, packaged product, I'm not your candidate," Simon stressed in the first Democratic debate in Houston on July 1. "If you want someone who levels with you and whom you can trust, I'm your candidate." Simon claims he's the candidate of integrity and courage, the one who refuses to tailor his positions to the prevailing political wind.

UNFORTUNATELY, a Simon victory, like Reagan's in 1984, would be a triumph of image over substance. Even though many voters disagreed with Reagan on particular issues, they supported him anyway with the idea that he would at least stand firm for something. And few paid enough attention to what that something was, or even to how much his convictions really meant to Reagan. So it is now with Simon. As David Axelrod, who managed his Senate campaign, told the New Republic, "Simon's greatest strength has nothing to do with issues. People respond to something in him that says, 'This isn't your normal bullshit politician.'"

Yet for all his talk about being authentic and honest, Simon has not leveled with the American people. On the one hand, he advocates $71 billion in new domestic entitlements; on the other, he strongly supports a balanced budget amendment. What he hasn't explained is how we can have both.

The nearest he has come to an explanation is the incredible assertion that an $8 billion new jobs program would take care of everything. Not only would the program guarantee every American a four-day-a-week job, Simon says, but it would also result in enough new tax revenue to balance the budget. He has repeatedly argued that, for every percentage point reduction in unemployment, the deficit falls by $30 billion. While appealing, this claim is really just a way to avoid discussing hard political choices, such as a tax increase.

"The figures are there," Simon insisted in last week's NBC debate. But where are they? The most recent major federal jobs program, the Emergency Jobs Act of 1983, cost $4.5 billion while providing only 35,000 net jobs, or $128,000 per job. At this rate, Simon's scheme to take 7.2 million Americans off unemployment roles would cost $902 billion. Even with a more reasonable cost per job--even with a ridiculously low cost per job--it's hard to see how the new tax revenues will eliminate the $148 billion deficit.

DEMOCRATIC rivals are right to denounce Simon's "solution" as "neo-voodoo" economics. Congressman Richard Gephardt, a supporter of the disastrous 1981 Reagan tax cut, had what for him was an unusual moment of insight during Tuesday's debate when he called Simon's ideas, "Reaganomics with a bow tie."

Moreover, for all his talk about political courage, Simon has yet to demonstrate any when it comes to foreign policy. Despite his habit of comparing himself to Harry Truman and John F. Kennedy, Simon's views are more in line with the quirky fringe that's so critical in the lowa Democratic caucuses: huge cuts in military spending, no aid to the contras, U.N. handling of the Gulf crisis, an end to SDI research and an immediate ban on nuclear testing. These ideas are not all necessarily bad, but they are when the advocate, like Simon, has put forth no course of action to be followed if the Sandinistas break the Arias plan, or if the Soviets violate the new arms control agreement.

For all his talk about integrity and courage, Simon's running a presidential campaign while saying very little that's substantive about issues that matter. Maybe that should be a character issue in itself.