KEENE, NEW HAMPSHIRE -- It could change in the next five months, but right now, voters in the first presidential primary are preoccupied with matters in their own backyard.

This is good news for the principal Republican contenders, George Bush and Robert J. Dole, both of whom are flapping around on foreign policy flypaper of their own manufacture.

The vice president, who is running as a seasoned world statesman, is reduced to bragging that he was "out of the loop" on the Reagan administration's premier embarrassment, the Iran-contra mess. The minority leader is trying to extricate himself from a cutthroat aside about a "little three-day invasion" of Nicaragua. He has since recanted an indiscretion that has caused his rivals to cackle about the "old Dole."

But as of this writing, Granite Staters are tuned out of Managua, Tehran and even Washington. They are brooding about affairs within their own borders: growth, development and, above all, the future of Seabrook, their luckless, impoverished, unplugged nuclear plant on the beach of Hampton.

Seabrook's lethal content has been tested at the polls. Last year the popular incumbent Republican governor, John H. Sununu, came within eight points of defeat by an obscure Democratic challenger Paul McEachern, who campaigned exclusively on a pledge to keep the plant closed.

Since then, the Seabrook stew has thickened. The utility, Public Service of New Hampshire, seeks a 15 percent rate hike as the only way of avoiding bankruptcy. It is further asking the state Supreme Court to strike down a law that forbids passing on a CWIP (Construction Works in Progress) tax, so the utility can charge rate-payers for Seabrook's initial astronomical costs.

On the Democratic side, Seabrook is moot. Massachusetts Gov. Michael S. Dukakis is a serious presidential contender because he said no to Seabrook, all but ensuring himself an early primary victory. He has vetoed evacuation plans that would affect the six Massachusetts towns within a 10 mile radius of the plant. The other candidates have fallen in line behind him.

But it looms over the Republican scene because Sununu, Seabrook's most adamant and militant booster, is Bush's campaign manager in New Hampshire. His endorsement brings him a vigorous organization, but considerable radioactive baggage.

Jack Kemp, who runs a distant third to Bush and Dole, has understood that an issue so clearly involving death and taxes would be the very thing for an underdog. He has wrapped his campaign around the plant. He specifically and ardently opposes the CWIP tax, the rate hike and a reduction of the 10-mile radius.

Kemp's hope is that anti-Seabrook voters, wanting to send a message to Sununu, who is running for an unprecedented fourth term, would take it out on his candidate, Bush.

"That's part of our strategy," says Kemp adviser Ed Rollins.

Bush, an advocate of nuclear power, who wishes that local state and utility authorities would settle their differences under the guidance of the Nuclear Regulatory Commission, has tried to sidestep Seabrook. Last April, when asked about the hotly contested 10-mile radius question, he professed ignorance. It turned out he had been briefed by the governor and by another local backer, Rep. Judd A. Gregg.

Kemp's New Hampshire chairman, former state Supreme Court judge Charles G. Douglas III, says cuttingly, "Bush has the same problem with Seabrook that he has with Iran-contra -- a memory that has faded to the point where he can't handle the presidency."

Gregg doesn't think Granite Staters would try to punish Sununu through Bush. "I don't think Republicans would throw away a presidential vote on that."

Tom Rath is a national adviser to Dole and a considerable figure in New Hampshire politics because of his successful management of Sen. Warren B. Rudman's fortunes. He says of Seabrook, "This has the capacity to overwhelm larger national issues because it's the one the electorate feels most intensely about."

In his speeches, Dole talks of "safety, safety, safety."

Public Service of New Hampshire has launched a $250,000 ad campaign warning of layoffs and service failures if it can't get more money. A public hearing on whether to reduce the evacuation zone is scheduled for next week. Until these vital matters get sorted out, Daniel Ortega, Ayatollah Khomeini and Mikhail Gorbachev will have to stand in line.

Chernobyl may have settled the future of nuclear power in this country but, odd as it seems, the fallout may still be drifting onto the field of the first presidential primary.