BOSTON -- Ira Jackson has the happy heart of a social reformer and the merciless soul of a tax collector. As reigning head of the Massachusetts Department of Revenue, this engaging and hard-driving man has -- let us be honest here -- gotten his kicks seizing a Rolls Royce, putting a lien or two on a yacht and scaring up some $268 million last year in delinquent taxes.

So the fact that child-support payments in this state have just come under the wing (or eye, or claw) of his tax department is of more than casual note. As of July 1, any parent who is late, or lax or outright recalcitrant in making payments is inviting the scrutiny of this agency and, eventually, its computers. Computers that, he likes to recall, never sleep.

''I don't want to sound menacing,'' says Jackson, who looks more the cherub than the avenging angel, ''but we intend to make some very visible actions.'' There is a ''Make My Day'' gleam in his eyes, as if he were just waiting for a sports superstar or corporate biggie to miss a payment.

At the moment, Massachusetts stands out as the only major state using its tax department for child-support enforcement. But Jackson's zeal is not unique. It's indicative of a change in attitude -- a change that may not exactly be sweeping the country, but is chugging across it at a decent rate of speed. There is a re-emerging get-tough approach toward parents who walk out of their kids' lives, letting them slide down the economic chute.

These days, virtually every plan to help kids out of poverty, every plan to overhaul welfare, is geared toward the new old-fashioned notion that parents are responsible for their kids. Plans like the one Sen. Daniel Moynihan introduced in Congress on July 21 have the same two crucial components: job and education programs for single parents on welfare and streamlined programs to enforce child-support payments.

For a long time, says Jackson, ''society simply went brain dead'' on the subject of getting dads to pay. ''It was like drunk driving or tax evasion,'' he says, returning to his favorite analogy. ''We condoned it, we wrung our hands over it, we allowed it. Only three out of 10 fathers were doing what they were supposed to be doing, paying an average of $2,300 a year, the cost of putting up one dog at a kennel.'' A man was more likely to get arrested for a traffic violation than for a child-support violation.

Child support suffered from its place in the messy wrangling between adults. It was just money to be argued over. But during the 1970s, the rate of divorce and single parenthood rose and with it the child-ization of poverty. Welfare critics noted that 87 percent of recipients of Aid to Families with Dependent Children were on the dole because of inadequate child support. And many were once middle-class.

One study in Colorado found that two-thirds of fathers paid more in payments for their cars than for their kids. California research found that, in the year after divorce, the standard of living of the mother and children had gone down 73 percent, while the father's had gone up 42 percent. Still another study proved, not surprisingly, that the stricter the enforcement of child-support payments, the higher the rate of compliance.

''We're now saying the issue is not parents, it's kids,'' says Jackson, reflecting a view built into the 1984 federal law requiring state child-support guidelines. ''We're not the government intervening between husband and wife but protecting kids.''

Few states have set up as aggressive a posture as Massachusetts has, but a standard is emerging that says children should not live measurably worse than their parents. This policy has its opponents, especially among men who resent transferring money to their ex-wife's household. There is resistance by men who feel that support checks are their only leverage in the power struggle for visitation rights.

Public policy makers have trouble staying above this fray. But a pro-kids, law-and-order coalition has made enforcement a popular position for politicians of all stripes. Not the least of them is the head taxman of Massachusetts, whose close friend and governor, Michael Dukakis, is running for president as a tough-minded liberal.

''A thousand years of common-law tradition says you are liable to support your kids,'' adds Jackson. ''We lost perspective and we're going to turn that around.'' It will take time and some help from the legislature to get the program up to megachip speed. But anybody who doubts Jackson's ability to ''persuade'' people to pay what they owe ought to chat with some recent converts to the overweening joys of paying taxes, right on time.