MANCHESTER, N.H., JAN. 23 -- When Rep. Richard A. Gephardt (D-Mo.) returns to New Hampshire Sunday, Mark Longabaugh, state director of his presidential campaign here, expects him to attract more attention than usual.

Gephardt has surged to top of the most recent polls in Iowa, making him momentarily appear as the potential main challenger to front-running Massachusetts Gov. Michael S. Dukakis in New Hampshire.

"The Boston media will be all over him like dogs in heat," Longabaugh said.

It is one measure of the unpredictability of the Feb. 16 New Hampshire presidential primary that polls taken in a state halfway across the country are watched as closely as polls and political organizing efforts here. Until Iowa Democrats caucus on the night of Feb. 8, the script will not be set for the final, frantic rush leading to the New Hampshire vote eight days later.

As a result, when the seven Democratic hopefuls gather at the University of New Hampshire in Durham on Sunday for their first statewide, televised debate, they will be viewed by an unusually volatile electorate that is only beginning to focus on the presidential contest.

Some campaigns report telephone and door-to-door canvassing efforts are finding 70 percent or more of the voters who say they are undecided. The actual number of undecided voters is probably considerably less, but there is widespread agreement among Democratic campaign operatives that, beneath the Dukakis lead, the situation has remained fluid.

"Whatever the numbers are, the vast majority of people haven't decided and a significant portion of every candidate's support is soft," said Steve Cancian, state campaign director for Jesse L. Jackson.

As the governor of neighboring Massachusetts, Dukakis has the largest and best organization in the state as well as a clear-cut lead in public opinion polls. A Los Angeles Times poll completed Thursday showed Dukakis with 37 percent of the vote, well ahead of Sen. Paul Simon (D-Ill.), who had 19 percent.

The poll showed former Arizona governor Bruce Babbitt moving into third place with 13 percent, followed by Gephardt, 8 percent, former Colorado senator Gary Hart, who plunged into a tie with Jackson at 6 percent, and Sen. Albert Gore Jr. (D-Tenn.), 5 percent.

In a business in which lowering expectations has become an art form, even Charlie Baker, Dukakis' New Hampshire campaign director, said, "Mike Dukakis will win here." But who will be his main challengers among the other six? It is here that the Iowa results are expected to be critical, conferring an aura of "viability" on one or more of the others and guaranteeing them heavy news coverage in the last critical week of the New Hampshire campaign.

Gephardt and Simon, the midwesterners in the race, as well as Babbitt, the longshot candidate who has invested so much in Iowa, have the most at stake. All three are credited with New Hampshire organizations that could take advantage of a strong Iowa showing, but all three will not have the opportunity.

"Whoever loses there becomes a nonfactor," Baker said.

Longabaugh argues that saturation coverage of the Dukakis campaign by the Boston news media -- which reaches a large portion of the New Hampshire electorate -- is affecting the New Hampshire political landscape. The first of the polls showing Gephardt rising to the top in Iowa was commissioned by WBZ-TV in Boston. The night the results were reported, Longabaugh said, "the only two people in the story were Dukakis and Gephardt."

Simon enjoyed a similar boost here this fall when he became the temporary Iowa front-runner. He rose to double digits in New Hampshire polls "on the basis of his perceived viability in Iowa," said Michael Muir, Babbitt's campaign director. But Muir, who described Simon as "a great first date," and other rival campaign managers suggest that the Illinois senator may be particularly vulnerable to anything less than a clear-cut Iowa victory.

Two other factors have further muddled the New Hampshire contest. One was former Colorado senator Hart's reentry into the race. Hart is a kind of unofficial "favorite son" in New Hampshire, where his stunning 1984 upset of former vice president Walter F. Mondale almost propelled him to the Democratic nomination.

Despite Hart's numerous problems and his plunge in the polls -- from second to Dukakis in a Gallup poll taken earlier this month to a distant fifth-place tie in the Los Angeles Times survery -- he is thought likely to retain a loyalist base here of perhaps 10 percent of the voters. Moreover, because of the controversy surrounding his candidacy, Hart may not need a strong Iowa showing to attract attention in the critical week between the Iowa and New Hampshire contests.

The other factor is Jackson, who won 5 percent of the New Hampshire primary vote in 1984 with virtually no organization. This year, Jackson has 22 full-time paid campaign workers and seven offices in New Hampshire and he is planning a modest radio and cable television advertising effort. Cancian said they hope at least to double Jackson's support to 10 percent, an objective that others said may be within reach.

If Hart and Jackson between them win close to 20 percent, and Dukakis retains the support of at least one-third of the voters, the other four candidates will be left to fight over 50 percent or less of the New Hampshire electorate.

One candidate who apparently has calculated that this does not leave enough maneuvering room is Gore, who has retained a staff of 18 full-time workers and six offices, a larger presence than Babbitt's. Gore hoped to finish a respectable fourth or even third in New Hampshire, giving him a boost heading toward the March 8 "Super Tuesday" contests in his native South. But that strategy is being reevaluated, according to Richard Nicholson, his state campaign director; Gore may spend less time and money here than originally planned.