Animosity is the oxygen of politics, and many conservatives savor their animosity toward Massachusetts. Today this state's economy is a gaudy spectacle and as lacerating to conservatives as, say, pornography.

Massachusetts' prosperity is, at least in the eyes of, say, Texas (unemployment around 11 percent), obscene. Massachusetts' unemployment is 3.7 percent. That is too low: labor shortages are inhibiting growth. New workers are on the way, drawn by wages up 29 percent in three years. There are growing pains: the median price of a house in the Boston area, up 70 percent in two years, is $149,000, about $70,000 above the national average. But personal income in Massachusetts is fourth in the nation, behind only Alaska, Connecticut and New Jersey.

Many conservatives loathe ''The People's Republic of Taxachusetts,'' partly because Harvard is here, partly because the state voted for George McGovern, partly because until recently it was a paradigm of the Frost Belt in decline -- a high-tax welfare state. Now, in a fresh affront to conservative sensibilities, Massachusetts' boom coincides with the tenure of a highly popular Democratic governor whose defeat in 1978 was an early tremor of the conservative volcano nationally. His return to political prosperity in 1982 was especially insufferable because he had spent part of his exile at . . . Harvard.

When asked the reason for Massachusetts' boom, Gov. Michael Dukakis unhesitatingly answers: ''A great governor.'' Then he laughs. Actually, he ranks himself third on the list of Massachusetts' blessings.

First is the fact that Massachusetts is planted thick with colleges and universities -- 120 of them, a garden of talents. Second is the state's quality of life -- this city, Cape Cod, the Berkshires. People come here to school, acquire skills and stay. Half the 2,000 PhDs produced here each year stay. Massachusetts Institute of Technology graduates have started more than 1,000 businesses.

The third cause of the boom, says Dukakis, is, well, aw shucks, the governor's aggressive industrial policy, involving state spending on infrastructure (roads, schools, etc.), and loans and other subsidies to encourage new industries to rise on the rubble of the old shoe and textile industries. Hundreds of businesses are in partnership with the state government. But conservatives should mind their manners about reviling this: if this is socialism, socialism works.

Actually (brace yourselves, conservatives), a fourth cause of Massachusetts' prosperity is another government: Ronald Reagan's. According to one estimate, 16 percent of the state's growth in the Reagan years has resulted from defense spending. Massachusetts ranks 11th among the states in population but fourth in defense contracts. Massachusetts' liberalism is not too fastidious to welcome 7.7 billion Pentagon dollars a year.

A fifth cause of the state's prosperity is the conservatives' club for beating Dukakis. It is Proposition 2 1/2.

An indispensable ingredient in political argument is the post hoc, ergo propter hoc fallacy. (The rooster crows, then the sun rises, so the crowing caused the sunrise.) Conservatives say Dukakis is the crowing rooster. Dukakis might say the same of Proposition 2 1/2, if he mentioned it.

In 1979, Massachusetts had one of the nation's highest tax burdens. In 1980, two years after California's Proposition 13, Massachusetts voters passed Proposition 2 1/2, limiting property taxes. Today Massachusetts is economically robust. Ergo. . . .

Clearly Proposition 2 1/2 helped improve Massachusetts' economic climate a lot. Richard Brookheiser, the cutting edge of National Review's conservatism, says that because Dukakis opposed 2 1/2, and Reagan and the defense buildup, Dukakis cannot claim credit for his state's boom: ''You might as well give Stanley Baldwin credit for D-Day.''

But you might as well admit that it is hard to establish causal connections in complex societies. And in politics, if you are sitting there when good things happen, you get credit. Besides, when it comes to tax-cutting, Dukakis is born again.

In 1974, he was elected governor. Promising not to raise taxes, he imposed the state's biggest tax increase. In 1978, the voters chucked him out. Chucked back in in 1982, Dukakis II has used an amnesty for delinquent taxpayers and a crackdown on cheats to help finance repeal of the 7.5 percent income surtax imposed eight years ago by a vague memory known as Dukakis I.

Massachusetts' GOP, known as the Chernobyl of the national Republican Party, has not won a statewide race since 1972 (Sen. Ed Brooke). It is not even contesting most congressional and state legislative races, and the two leading candidates to oppose Dukakis evaporated in the heat of scandals. When he wins in a waltz, will he think about running for president? After all, New Hampshire is next door.

Dukakis laughs, saying that a lot of people moved to New Hampshire to get away from him. Note that that ''answer'' is not a ''no.''