NEW HAMPSHIRE Gov. Meldrim Thomson Jr. caused a small stir last week by ordering the flag at state buildings flown at half-mast on Good Friday "to memorialize the death of Christ." After a flurry of legal actions, Mr. Thomson's order was blocked, and flags in Concord were still flying high - by a hurried Supreme Court vote of 5 to 4.

That flap may sound a bit bizarre, but it was tame next to some of Mr. Thomson's contributions to the public scene. The New York Times recalled the other day, for instance, that once a motorist made "an obscene had gesture" at Mr. Thomson, and the governor had him barred from the state's roads for 90 days. And then there was Mr. Thomson's ideal of giving atomic weapons to the state's National Guard . . .

So far Mr. Thomson has not ordered a nuclear strike. But he does use heavy weapons of invective and intimidation freely against welfare recipients, anti-nuclear-power demonstrators and the like. One frequent target is his state's senior senator, Democrat Thomas J. McIntyre, now under assault by the "New Right" for supporting the Panama Canal treaties. "In all of this nation." Mr. McIntyre said last month, "there may not be two more recklessly belligerent public figures" than Mr. Thomson and his ally, Manchester Union-Leader publisher William Loeb.

Clearly, Mr. Thomson is not your average conservative Republican. And he's distinctive in another way: For all his nastiness and quirks, he has managed to do somethings most politicians only promise. He has kept New Hampshire's taxes very low. The state has no sales tax or income tax. Its economy is the fastest-growing in the Northeast - partly because people and investment keep migrating from high-tax Massachusetts next door.

That's why Mr. Thomson is flying hihg and may well be a shoo-in for a fourth statehouse term this fall. That's what he means when he campaigns, "Vote for Mel Thomson for what you moved to New Hampshire for." It goes to show what really moves some voters - and what some taxpayers will put up with when the price is right.