For an American taxpayer, Keith Hunt is a happy man. The 47-year-old former Massachusetts resident has a good job, a four-bedroom home in the scenic Merrimack Valley and plenty of skiing just a short ride from his door. Most important apart from federal income tax and local property taxes, he pays almost no taxes.

"I'm really enjoying it," he tells visitors here.

Hunt escaped the tax nite simply by moving 30 miles north - to New Hampshire. The Granite State is alone among the 50 in having neither a broad-based income tax nor a statewide sales tax. When Hunt's firm opened a new plant in nearby Nashua, N.H., last June, the chief engineering manager could have stayed in Westford, Mass., and commuted. But he chose to move to Amherst - mostly to save on taxes.

As a result of the move, Hunt figures this year he'll save almost $900 in state income and sales taxes he otherwise would have paid if he'd stayed in Massachusetts. And the Hunts are paying $800 less in property taxes - even though their house here is larger than their place in Westford, with twice the lot-space.

"It's worked out very well," Hunt says with satisfaction.

The Hunts weren't the only Massachusetts family to be lured across the border recently by New Hampshire's bargain basement tax laws. According to the state's figures, more than 25,000 persons have made the same sort of move in the past 6 1/2 years - part of an influx that has swelled the state's population by 21 per cent. Many have come with companies that have built new facilities here.

In fact, since the boom accelerated in 1971, some 516 companies from around the United States have located new plants inside New Hampshire, creating 20,950 new jobs and 10.6 million square feet of new construction - plus thousands of new restaurant and other service jobs. "It's really tremendous," glo ats Paul H. Guilderson, New Hampshire's director of industrial relations."

Not everyone, however, is as enthused as Guilderson about New Hampshire's free-spirited tax structure. Over in Massachusetts, blunt-spoken Gov. Michael Dukakis fumes that the disparity in tax rates gives New Hampshire an unfair advantages over neighboring states. Of the 516 firms that have built here in the past six years, 106 have come from Massachusetts.

As if the tax incentives weren't enough, New Hampshire has compounded the problem by offering Massachusetts residents Sunday store hours and cheaper liquor and cigarettes, enticing droves of shoppers every weekend. (The toll plazas along the major freeways leading in from Massachusetts all have New Hampshire state liquor stores built along the median).

Howard N. Smith Massachusetts' Secretary of Economic Affairs, estimates that the loss in retail sales may have hurt his state even more than the plant movings.

"There's no question the Merrimack Valley retail trade in Massachusetts have suffered," he says. Smith concedes New Hampshire has sapped away much of the potential new industry from the Midwest and Southeast.

As might be expected, the drainoff of jobs and sales has brought the two jurisdictions to a state of economic warfare over the past two or three years - often with bitter results. (In one unseemly gesture, New Hampshire once threatened to impose an income tax on the handful of Massachusettans who work in the Granite state. It since had retreated on that issue.)

To be sure, bargain tax rates aren't the only factor that has drawn Bay State dwellers to New Hamsphire recently. Local planners also cite the northward creep of the Boston suburbs, the opening of downstate New Hampshire freeways, the state's easy access to Boston's airport, a stable labor market and the newly fashionable back to-the-land movement.

But officials on both sides concede the tax break is the big turning point in most instances. A case in point is the new wheelabrator-Frye Co. facility, built in nearly Hampton. Although company spokesmem inside the tax factor wasn't dominant in the firm's decision, critics note the move involved only the firm's headquarters operation - replace with high-income executives.

The figures are indisputable. According to the latest tally, for 1975, New Hampshire's absence of state income and sales taxes gives it the lowest state tax burden in New England. New Hampshire residents pay an average of only $503 per capita, compared to $786 in Massachusetts. The average for the United States as a whole that year was$667.

The result have been dramatic. While the rest of New England barely has recovered from the double-digit unemployment of the 1974-75 recession. New Hampshire boasts a jobless rate of only 3 per cent - one of the lowest in the nation. The Massachusetts rate is 5.8 per cent. And the influx has bloated state and local property tax revenues here by an estimated $4.7 million.

Predictably, New Hampshire's light fisted Yankee tax stance has around widespread clucking from liberals and many academics, who contend a state must have a broad-based tax of some kind nowadays or risk bringing on a fiscal disaster. Tax experts warn if a state shuns sales or income taxes, it either must pare services drastically or shift the burden to property taxes.

New Hampshire's maverick Gov. Meldrim Thomson Jr. disputes this assessment. Thomson argues that the increases in government costs can be borne easily enought by the burgeoning business tax revenues brought in by the influx of new industry and no new taxes are needed. (New Hampshire has a limited income tax, but it only affects dividends and interests.)

The silver-haired conservative Republican delights in rubbing Massachusetts nose in the dirt by using the disparity in tax rates to paint his southern neighbor as a spendthrif. Massachusetts now has one of the highest tax burdens in the nation. The reason, Thomson asserts repeatedly, is that it insists on maintaining overly generous social programs.

New Hampshire officials are fond of quoting a 1975 study by Dartmouth University professors Colin and Rosemary Campbell that contends service levels in the state are no worse for lacking of an income tax. The Campbell compared New Hampshire with neighboring Vermont on a variety of social measures - such as students' scores on college aptitude teste - and found little real difference.

In a sentiment that clearly reflects Thomson's thinking. David Rines, the governor's chief economic adviser, says not having an income tax effectively "puts a bid on how much is going to be spent." If you have money available, he sniffs, "you're just going to look for ways to spend it - like Massachusetts does."

In the past several months, however, there have been signs that may be changing. For one thing, the new influx of Massachusetts dweller most of them upper-income executives and technicians has created a demand for sharp increases in services - a burden whose cost has fallen primarily on local property taxes. Many smaller communities have been completely overwhelmed.

The Southern-tier township of Merrimack, for example, was delighted at first when it began acquiring major new plant facilities. A hamlet of 3,000 just 17 years ago. Merrimack now is the site of dozens of new factories or expansions - among them the Anheuser-Busch brewing company, the giant Digital Equipment Corp. and General Electric Co.

But the demand for new services and equipment has pushed Merrimack's property tax tate from a moderate $44.60 for each $1,000 of assessed valuation in 1974 to a whopping $63.50 in 1977 - a 424 per cent increase. Townspeople now are fretting over a demand by Digital for a new $16 million highway interchange so its employees can have easier acess to the plant.

Many of the transplants from Massachusetts are demanding added - or better - services than New Hampshire communities traditionally have provided.Kenneth Scalon, a Waltham, Mass., native who moved to Amherst recently, laments that "you don't get the same type city service" here. Amherst has no municipal water system, refuse collection of high school.

As a result, many New Hampshire communities now find themselves so strapped they're beginning to turn to large-lot zoning as a defense against the influx of newcomers. Several of the towns in the Southern tier area already have mandated 1- and 2-acre lots for each new house. Just last month, tiny Raymond, N.H., won an appeals court decision upholding minimum 10-acre lots.

Guilderson is beginning to urge newcommers to spread beyond the Southern tier area, which has absorbed most of the influx, into northern and western New Hampshire. "We have to have more geographical dispersion," he says.

"If we don't think we have room for an industry, we urge them not to come. Nowadays, we tell more Massachusetts firm that not to stay where they are."

The fact is, despite the Campbell comparison with Vermont, New Hampshire is substantially behind Massachusetts in spendding for social programs. Massachusetts' per capita for outlays are 1.7 times New Hampshire's for educationn, 1.3 times as large for health and hospitals and 2.7 times for public welfare. New Hampshire is ahead only on highways and natural resources.

Massachusetts officials have been underscoring the differnce with ferocity recently. Dukakis sneered in an interview recently that "New Hampshire is a great state to go to - provided you don't have a retarded kid, an alcohlic father or a kid you want to send to kindergarten." And some Massachusetts dwellers are beginning to catch on.

Critics also complain New Hampshire's reliance on property taxes places the brunt of its tax bruden on the poor. Figures published in a Western Kentucky University study show in 1974 New Hampshire's state and local tax burden is only 5.1 per cent of personal income for families in the $50,000 and up bracket. But for those earning $10,000 or less, it was 8.2 per cent. Analysts say the percentages haven't changed since.

Despite Thomson's contentions, many critics say New Hampshire hasn't kept as fiscally sound in the absence of a broad-based income or sales tax as the governor would have everyone think - and indeed, it may be in something of a fiscal box. To be sure, the state still has a legally-balanced budget. But it's balanced only by a thread.

Last session for example, in the face of Thomson's opposition to an income tax, state legislative leaders had to resort to a patchwork of revenue raising measures to avoid a deficit - small, but significant 1 per cent increases in the state's business profits and room and meals taxes, and a 0.75 per cent boost in the income tax on interest and dividents.

The state took all the extra revenues from the room and meals tax boost, not passing them on to hard pressed localities. Even so, the governor refused to approve the final version: he just let it become law without his signature. "It's a phony patchover," snaps Sen. C. Robertson Trowbridge, chairman of the Senate Finance Committee.

Ironically, the legislature's actions have narrowed the tax gap somewhat. Although New Hampshire's new 8 per cent corporate tax rate still is below Massachusetts' 10 per cent by levy on business, the Granite State's room and meals tax is the same as Massachusetts' 6per cent. And skyrocketing local property taxes are coming closer to those south of the border.

Moreover, Massachusetts has taken some steps of its own that, while relatively small in comparison to the total, may help stem some of the drain of the jobs and consumers. At Dukakis' insistence, the Bay State legislature voted to lift the Sunday blue laws during the Christmas season - a move the administration hopes will pave the way for year-round Sunday shopping.

And the governor pushed through a liberalization of advertising restrictions on liquor stores that now allow big chain operations to complete with New Hamsphire's border boozevendors. Smith says the state also have stepped up its efforts to get instate companies to expand their facilities at home.

But the disparity still is enormous. A recent report by the Advisory Commission on Intergovernmental Relations ranks Massachusetts number two in the country (just behind New York) in tax burden "pressure" on its constituents - with New Hampshire at the bottom of the list. Dukakis claims Massachusetts can't cut taxes more because of its budgetary commitments.

Musing on the subject last week, Dukakis declared boldly that the New Hampshire situation has reached a turning point, and that Thomson soon would forced to turn to a broad-based tax or face fiscal defeat.

"The New Hampshire problem for us is now ancient history," he said. "The drain of industries now has slowed to a walk." Thomson, who was in Taiwan last week on state business, could not be reached for comment.

Rep. George B. Roberts Jr., speaker of the New Hampshire House of Representatives, agrees. Roberts has tried five times in the past few years to push through a broad-based state income tax but has failed every time. Now, he says, "We're about to the point where we can't passed any more of these costs onto the property tax. We've about had it."

But other officials aren't so sure - even the state's few liberals, who have been urging the adoption of an income or sales tax.

"It's still going to be several years off," predicts Rep. Susan McLane, chairman of the New Hampshire House Ways and Means Committee and an advocate of a new broad-based tax machanism. "The governor still gets cheers wherever he goes."

Thomson consistently has made the no-inconme-tax pledge the centerpiece of his gubernatorial campaign - almost inevitably drawing cheers from the majority of the state's voters. Although not all New Hampshire residents share Thomson's view, enough do so the poly is effective. Even the governor's Democratic opponents have adopted a no-tax plank.

Still, Massachusetts' Secretary Smith is confident. Sooner or later, he says, New Hampshire will begin to realize that it can't continue shoring up its budget with smaller measures and will have to turn to a broad tax to finance its services. The tax situation in New Hampshire "is sowing the seeds of its own slowdown," he says. "Time is our side."