With two weeks left before Iowa caucus-goers begin voting for president, none of the applicants for the job in either party has come up with what Madison Avenue would call the distinctive selling proposition: a big, catchy message.

"There aren't any magic seven words out there," mused Ed Rollins, who managed a campaign in 1984 -- Ronald Reagan's reelection -- that needed just five words to capture its core appeal and the country's mood: "It's morning again in America."

Strategists for both parties agree that those won't play in 1988, nor will 1980's winning "Get the government off our backs," nor 1976's "A government as good and decent as the American people." Nothing new has come along to take their place.

It's still early in the election year, of course, and the search for a message remains muddied by voters' apparent uncertainty about what they want. National polls find voters suspended between prosperity and anxiety -- agreed that the country's next big challenges are to compete better in the world economy and take better care of those at home left behind by the "Reagan Revolution" -- but torn over how best to achieve either goal.

Of all the candidates in both parties, the one whose message has the most energy currently is Rep. Richard A. Gephardt (D-Mo.). He is touching raw nerves in Iowa by telling workers and farmers they are getting the shaft from trading partners who won't open their markets and corporate giants who are profiting from the status quo.

Until earlier this month, when he honed his appeal down to its angry nub of economic nationalism and anticorporate populism, the 46-year-old chairman of the House Democratic Caucus had been all but given up in Iowa. Now he's the narrow leader in the polls, and many Democratic strategists think his superbly timed surge can carry him to victory in the caucuses on Feb. 8.

But they question whether his message can travel outside a hard-pressed farm state or beyond a core Democratic blue-collar and farm audience. Even in Iowa, according to the polls, Gephardt has picked up little support among white-collar Democrats.

"It's a narrow way of running for president and it is going to require a reinvention of message as he goes into other states that are better off," said a top aide for a rival Democratic candidate, who asked not to be identified.

Even if Gephardt has only latched onto the fragment of a presidential-scale message, however, he has provided the Democratic field with something it has lacked until now: a clear cleavage around a large set of questions.

To the surprise of many, the core Democratic debate of 1988 now seems likely to be a replay of what it was in 1984, in the showdown between Walter F. Mondale and Gary Hart.

It is an argument between "neo-liberals" who say the nation's response to a changing world economy must be to develop growth policies that master change, and "old Democrats" who say the first order of business must be to provide economic security for the victims of change.

The seven candidates understand this really isn't an either-or proposition, but they are using the shorthand of political campaign rhetoric to oversimplify.

Those who are hitting the hot buttons of economic security include Gephardt, Sen. Paul Simon (D-Ill.) and Jesse L. Jackson, while those in the growth camp include Massachusetts Gov. Michael S. Dukakis, former Colorado senator Hart, former Arizona governor Bruce Babbitt and Sen. Albert Gore Jr. (D-Tenn.).

"The road backwards is a road called protectionism," Hart told Gephardt in a debate Saturday in Ames, Iowa, in which the new-versus-old cleavage crystallized.

Gephardt's positioning in this debate is risky -- but if he can pull it off, it is potentially formidable. He has basically switched sides, and now wants the political benefits of both positions.

In his 11 years in the House, he has never fashioned himself a traditional Democrat in the Great Society-New Deal-Mondale-Simon mold.

As recently as 1985 -- when many Democrats were so cowed by the Reagan landslide that pollsters were telling party leaders that when voters hear Democrats talk of "fairness" in social policy, "they think it is a code word for giveaway" -- Gephardt founded something called the Democratic Leadership Council. It is a group of more than 100 neo-liberal, moderate and conservative elected officials who are determined to cast the image of their party as something other than a collection of aggrieved constituencies.

A year ago, the DLC put out a white paper on trade arguing that roughly 80 percent of the nation's trade imbalances are caused by uncompetitive factors in the domestic economy rather than by closed markets abroad. Gephardt spent much of 1986 and 1987 on the presidential campaign trail talking about fixing these problems by investing in education and training, and by changing management and labor practices in the workplace to give employees more of a stake in their companies' success. He lit no fires.

Now he is broadcasting a television commercial in Iowa in which he complains that if South Korea continues to insist on trade barriers that result in a $10,000 Chrysler K-car selling for $48,000 in Korea, then Hyundais should cost that much here. And he's shooting up in the Iowa polls.

The lesson? "What the so-called new-Democrats lack is applause lines," said Ann Lewis, a Democratic consultant. "The political insiders have been taken by surprise this year by the durability of the old message. They thought the electorate was ready to move beyond the party's traditional symbols, but first with Simon and now Gephardt, the voters are sending us a signal that they aren't."

At least that seems to be the lesson out of Iowa, where the candidates are competing for the allegiance of a small group of party activists who will vote in the caucuses.

Simon is the candidate most displaced by Gephardt's Iowa surge, and his camp has begun to fight back. Paul Maslin, Simon's pollster, derides Gephardt as a "fly-by-night populist" and David Axelrod, Simon's media adviser, says he "went overnight from Russell Long to Huey Long . . . and needs to have a rendezvous with his record."

The trade issue has imbued the Gephardt candidacy with a toughness and passion that his rather bland personality does not project on its own. He has gotten crisper and more confident on the stump; suddenly, he's a finger-pointing insurgent as he talks of "fighting the big boys" on Wall Street, Washington and in agribusiness board rooms.

When rivals point out that he is a member of the establishment that he's attacking, Gephardt tries to position himself as an insurgent insider -- someone who can shake up the system because he is a part of it.

However the Gephardt strategy plays out, it has the happy effect, in a Democratic field that wallowed unhappily and too long in the "character issues," of placing serious matters of national policy and direction at the center of the party's debate.

On the Republican side, that's the ingredient missing from the confrontation between Vice President Bush and Senate Minority Leader Robert J. Dole (Kan.).

Each camp believes that 1988 will be an election about fine-tuning, not change of direction. The Republican front-runners have no fundamental policy arguments with the status quo or, for that matter, with each other. It's a rule of thumb in political campaigns that if you can't have big fights, you'll wind up having nasty ones -- and that's exactly what Bush and Dole got into this month.

The spectacle of the vice president and the minority leader bickering over who released his tax returns, whom the president calls first, and who started out poor in life has many Republican strategists worried that they are squandering their vaunted stature advantage over the Democrats.

"There is an arrogance on the Republican side that bothers me," said Rollins, who is campaign chairman for Rep. Jack Kemp (R-N.Y.). "It is a belief that we have the better candidates, they have the dwarfs, and it's just a question of whether Bush or Dole wins. If Republicans don't start putting together a message, we could be in trouble."

On the stump, Dole says he will be Reagan with a little more compassion; Bush says he will be Reagan with a little more education. But neither message acknowledges that the "morning again" appeal of 1984 is out of sync.

A recent nationwide survey taken for the World Policy Institute, for example, found that 82 percent of voters think that "other countries are showing less and less respect for America" (one of the reasons the trade message plays); that by 67 to 25 percent, voters think the U.S. economy has gotten weaker relative to other countries; and that by 59 to 14 percent, voters say investing in a strong economy is more important than investing in a strong military.

Those are not the attitudes that reelected Reagan by a landslide in 1984. Sooner or later, the Republican front-runners will have to face up to the changes.