In this last month before the Iowa caucuses, four Democrats have been running above 10 percent in polls. What messages have they been sending out? How have they been received in Iowa, and how sustainable will they be in later contests? Much of the answer comes from looking at their paid media (TV spots), because in the clutter of 13 candidates, paid media have been driving the numbers and giving voters a more vivid impression of hitherto unknown candidates than free media (coverage in newspapers and on TV) can.

Dick Gephardt's message was carefully calibrated late last year. The candidate who spent the most days in Iowa hired media makers David Doak and Bob Shrum, who are exquisitely sensitive to local idiom, and concentrated his $500,000 time buy beginning Dec. 26. His spots stress Gephardt's support of workers (his trade bill); farmers (production controls); and seniors (Claude Pepper testifies to his unyielding support for Social Security). With unflagging discipline, dressed often in his green down-filled jacket, Gephardt echoes the same themes in every speech.

The strategy can be attacked as pandering to well-organized and affluent groups. But it has clearly attracted supporters that Gephardt's long-nurtured organization hopes to turn out caucus night. "We're getting the elderly and the people with dirt under their fingernails," Gephardt coordinator Steve Murphy says, "spread pretty evenly across the whole state." If Gephardt wins Iowa, it will be the way many senators win their races: with a carefully contrived, cleanly executed strategy based on consistent emphasis of just a couple of themes.

But how will this Iowacentric message travel? Gephardt has never been a politician to turn on a dime: he is a planner, a plodder, a hard worker who in debates seldom deviates from his script. Low-tax New Hampshire and the hawkish Super Tuesday South are different terrain from Iowa. His $48,000 Hyundai ad may work everywhere. But if Gephardt, who has switched on national issues from abortion to tax cuts, is seen as adapting to local preferences after Iowa, he will be portrayed as changing his clothes in public -- always an undignified posture.

Paul Simon's message is steadiness. His first media flight, from mid-November to mid-December, propelled him up above 20 percent in some polls. David Axelrod's bio showed him as a crusading country editor, and another spot showed him on his back porch in Makanda, Ill., talking easily to the camera about his liberalism. He slipped some in December, as he was attacked for his budget arithmetic and was hurt by his lack of command in debates; his most recent TV spots, which went up (on the air) Jan. 29, show him in black-and-white stills and, in color, saying "my bow tie is kind of my declaration of independence." The idea is to stress his "character, strength and integrity," his Iowa coordinator Pat Mitchell says. But he's also been snapping at Gephardt's tax votes and position changes on the stump and in radio ads that began Feb. 5.

Simon's pleasant, corny demeanor and his old-fashioned message are perfectly attuned to the liberals who can remember when their creed was unfashionable and scorned by most of their articulate neighbors; and there are plenty of Democrats in elderly Iowa who go back to the 1950s. There are not as many in other states, especially in high-tech, low-tax New Hampshire, where few voters will applaud his anti-tax-cut votes, and in the South, where few share his faith that Mikhail Gorbachev wants to cut his defense budget as much as Simon does ours. Simon should do well in his home state of Illinois. But even if he does well in Iowa he will have to work to get there.

Michael Dukakis has sent several messages to Iowa over the past 11 months, all attractive, but none attractive enough to put him far out in front. The first is the "Massachusetts miracle": Iowa, with the nation's largest population loss in the 1980s, is as eager as any state for economic growth. The second has been legalism: his most scathing criticism, repeated over and over, of U.S. contra aid is that it violates the Rio Treaty and other international law. Iowans are sticklers for playing by the rules: this is one of the few states where Watergate cost Richard Nixon and Republicans votes not just in 1974 but in 1972.

These issues plus his good organization propelled Dukakis toward the front of the pack last summer and after his fall media buy. But he failed to surge ahead. So this month his campaign has been presenting him as a man of passion. Last year's spot made by Dan Payne showed a silver bowl being burnished by a Paul Revere-like craftsman. January's spots made by Ken Swope show horrifying pictures of Nicaraguan bodies and U.S. homeless children, with voice-overs from Dukakis saying we must stop the killing and house the homeless. The argument is that Dukakis is not just able -- Iowa Democrats already see him as a competent executive -- but that he burns to make peace and help the poor.

That argument will travel well in New England, if Dukakis finishes in contention in Iowa. And if he wins a clear-cut victory in Iowa he may have a reasonably uncluttered flight path toward the nomination, with Al Gore his only major competition and the South his problem spot. But if Dukakis finishes in the pack in Iowa, his passion may work against him in the hawkish South and among practical-minded voters in the big states (Illinois, Pennsylvania, New York) that follow.

Dukakis, who has spent 26 years thinking about state government and 11 months thinking about running for president, has still not come up with a plausible macroeconomic policy (no one else has, either) or a foreign policy that goes much beyond the moral indignation that has been an electoral liability for Democrats in recent presidential elections. Something more than his Iowa messages -- a national program, a big recession -- is needed to get him into the White House.

Bruce Babbitt has the trickiest message, and in the middle two weeks of January it seemed to be getting through: he was running in double digits in his own and other Iowa, and even New Hampshire, polls. But for the past week or so he has been back in single digits in public polls. His problem may be that his message runs skew to the usual lines of argument in American politics. He attacks contra aid harshly, but adds that American values of political freedom and market capitalism are prevailing in the world -- in contrast to Dukakis' and Simon's moralisms and Gephardt's East Asia bashing on trade. He backs a national sales tax to cut the deficit and calls for needs-testing federal programs, but wants to spend more, not less, on the poor -- in contrast to Gephardt's promises to well-placed farmers and seniors or Gore's steadfast defense of universal benefits and progressive taxes.

None of Babbitt's paid ads -- not the flight last May, showing him in flannel shirt sounding angry, not the crawl of press clips and man-on-the-street spots of January, not even his last-minute declarations that he alone is telling "the truth about what the future is going to cost" -- has succeeded in communicating his message or giving the vivid sense of his personality that voters seek in this most personal of all offices. This message, since it's not crafted specially for Iowa, may travel better than those of the three leaders. But there's something in it to irritate almost everybody (his sales tax won't enchant New Hampshire, his Central America dovishness won't help in the South), and he needs to finish well in Iowa to get people to listen.

One of the Democrats who has always been in single digits in Iowa, Albert Gore, might: his strong-defense, progressive-economic and innovation-scientific messages could give him wins in the South Super Tuesday and make him competitive in the big northern states that follow. Jesse Jackson can win lots of primaries if several Democrats stay in the race, since blacks make up one-quarter of the electorate in many southern states and Illinois. Gary Hart, forlornly telling audiences how he's been nurturing his new ideas for 10 years, has a message that seems doomed in Iowa and elsewhere. The question that must keep the Democrats nervous is whether those who could win in Iowa have developed anything better.

The writer is a member of the editorial page staff.