CONCORD, N.H. (AP) _ Dennis Clouthier is a conservative Republican - pro-Star Wars, pro-Contra aid and opposed to the U.S.-Soviet nuclear arms treaty. Yet in 1986, he voted for a liberal Democrat for governor solely because the GOP incumbent championed the Seabrook nuclear power plant.

The stalled, $5.2 billion project on New Hampshire's seacoast has been a leading state and regional issue throughout much of its 16-year history. Now its foes hope voters like Clouthier will make it an influential factor in the first presidential primary of the 1988 season - possibly ruining the presidential bid of Vice President George Bush.

All seven major Democratic presidential candidates are to some extent opposed to Seabrook, with Massachusetts Gov. Michael Dukakis playing a key role in blocking a license for the completed reactor. But there are some sharp distinctions among the five Republican aspirants.

Seabrook opponents criticize pro-nuclear Republicans at the bottom of the polls - former Delaware Gov. Pete du Pont and former television evangelist Pat Robertson. But their chief target is Bush, whose front-runner status in New Hampshire polls has been jeopardized by his third-place showing in the Iowa caucuses.

Bush views on Seabrook have echoed those of his state campaign chairman, Gov. John Sununu: Its fate should be left to the Nuclear Regulatory Commission, not state governors.

''George Bush is going to do terribly on the seacoast among Republicans because of Seabrook, and it could end up costing him the presidency,'' said Kurt Ehrenberg of Search '88. He noted that a little-known, anti-Seabrook challenger to Sununu in the 1986 gubernatorial primary won 22 percent of the vote statewide, and up to 45 percent in some seacoast towns.

To try to help fulfill that prophecy, Ehrenberg's group last week began airing radio ad on seacoast stations that concluded: ''If you don't want Seabrook, you don't want George Bush.''

Bush campaign aide Andrew Card disputed Ehrenberg's prediction.

''I don't think (voters) are that parochial,'' Card said. ''It will be an issue, but one of many, many issues in the primary - not a cutting issue.''

''Electing a governor and electing a president are two different things,'' said Paul Young of New York Rep. Jack Kemp's campaign. But he also speculated that Seabrook could have an impact if it costs Bush support on the seacoast.

Kemp, a strong proponent of states' rights, has asked federal regulators to hold up a low-power license for Seabrook before evacuation plans are developed that win the confidence of people within the plant's 10-mile emergency planning zone.

''I want to make clear, he is not against nuclear power - just for the health and safety of the people,'' Young said.

However, the Kemp camp has not been trumpeting its positions on Seabrook.

''I understand that. That's politics,'' said Mimi Fallon of the group Republicans Against Seabrook Station. ''They're afraid they're going to lose the people they already have on the other side'' who support the plant, said Fallon, who supports Kemp.

Another Republican hopeful, Sen. Bob Dole of Kansas, has suggested that the non-partisan National Academy of Sciences review Seabrook's evacuation plans because of a perception that the NRC favors the industry it is supposed to regulate. In December, Dole also asked the NRC to hold up low-power testing until evacuation issues are settled.

''I'd like to see Senator Dole go a little further, but I'm not knocking what he's done,'' Ehrenberg said. ''He's a tough guy to move on some issues, that's clear. He's a very careful politician.''

What irks the anti-Seabrook activists is Dole's insistence that governors should not have veto power over nuclear plants. But in an interview this month, Dole also said a governor ''has got to be certain that the rights of his people are protected.''

On the Democratic side, Dukakis is fighting in federal court against an NRC rule change that would allow approval of evacuation plans developed by utilities when governments balk. Dukakis tried to reinforce his standing with anti-Seabrook voters last week by holding a news conference with the reactor in the background.

Ehrenberg speculated that Dukakis' action against Seabrook may have gained him some early organizational support in neighboring New Hampshire, but that hasn't stopped the other Democrats from wooing the anti-Seabrook vote - in some cases, in spite of generally pro-nuclear records.

Former Arizona Gov. Bruce Babbitt said he served on the presidential commission that investigated the 1979 Three Mile Island accident and recommended the evacuation-planning rules that have become Seabrook's major obstacle.

Former Colorado Sen. Gary Hart said he sat on a congressional panel that helped write those recommendations law.

Jesse Jackson favors a rapid phase-out of all the nation's nuclear power plants and notes that he opposed Seabrook in his 1984 preidential campaign, before the Chernobyl disaster in the Soviet Union.

Sen. Paul Simon of Illinois calls Seabrook a ''white elephant'' that should not operate, and he held a news conference last week in the same place Dukakis did to criticize pro-nuclear votes by Rep. Richard Gephardt of Missouri.

Simon noted that a nuclear industry lobbying group said last year that Gephardt voted with the industry 53 percent of the time in recent years. But Gephardt says his votes came under a more vigilant NRC and he has learned since Chernobyl.

Sen. Albert Gore Jr. of Tennessee voted with the nuclear industry 55 percent of the time when he was in the House, but has taken a low-key position on problems at the Tennessee Valley Authority nuclear reactors.

Clouthier, the New Hampshire voter who is a quality-control manager, said he doesn't see Seabrook as an overriding issue in the primary.

''But I think they're all avoiding it like a hot potato because it is so controversial,'' Clouthier said.