I LOOK AT THE wedding pictures from 12 years ago and am struck by the blinding trust in those young faces. I suppose it is well that at that age, most of us don't yet know that such big promises can break.

A year later, the "Your First Picture" in Sarah's baby book shows a tiny, lovely creature a few hours old cradled in her father's arms, his face alight with wonder and welcome. Those promises can break, too.

Sarah's last conversation with her father began with her saying, "Hey, Dad, this is getting really stupid. How come you're not sending my money?" She said he explained that he had "a new family to support now" and couldn't always send her money, which was before he resumed payments.)

This new family includes two young children for whom, he said, no support is being paid. It's all very circular somehow: Sarah didn't get her child support because some other kids weren't getting theirs. She can join hands in a huge circle peopled by 10 million children in the United States today. About half the kids alive now will at some time during their growing-up years live only with their mothers, most of whom work to support themselves and their children.

Their fathers are at least equally obligated to provide support; most of them don't. National statistic indicate that close to 80 per cent of court-ordered child support goes unpaid. Those fathers who do pay support generally stop doing so after only two years.

As the incidence of divorce has risen to unprecedented levels in the past decade, so has the number of children financially discarded by absent parents. The number of "nonmarital" -- formerly known as out-of-wedlock -- children also has increased dramatically. Enforcing support in these situations often poses the additional problems of establishing paternity and obligation.

Families involved in child support conflicts where paternity or obligation is unquestioned -- the familiar nuclear families so many of us created in our 20s and saw come undone in our 30 and 40s -- still number in the millions. That's the circle of children my daughter has joined.

The Office of Child Support Enforcement (OCSE) of the Department of Health and Human Services was created in 1975 in response to major changes in marriage and family patterns. In the 1930s, Aid to Families with Dependent Children (AFDC) was established to help provide for children who had lost the support of a parent, usually because of the father's death. Now, however, the divorce rate and incidence of children born to unmarried parents have created a situation in which fully 80 percent of families receiving public assistance are eligible because a parent is absent, not dead.

According to OCSE's most recent annual report to Congress, the program "was created for the purpose of enforcing support obligations owd by absent parents to their children, establishing paternity and obtaining support. It is also one of the few government programs that helps needy families while also saving tax dollars." Indeed, in fiscal year 1981, more than 45,000 families in the United States were able to leave AFDC rolls as a result of enforcement activity. Succcess varies widely: Tennessee closed a total of 16,152 AFDC cases as a result of enforcement activity last year, while Georgia closed none.

Other aspects of the enforcement program differ significantly from state to state, too, which I learned in the process of trying to get Sarah's money.

Several different times over the past five years, Sarah's support has stopped coming. The lapse in payments lasted, each time, as long as it took me to find him. When found and confronted, he would resume payments.

The last time the support didn't come, I found out that Sarah's dad had remarried and moved to Texas, address unknown. I decided to let the courts handle the matter. A distinct feeling of relief accompanied that decision: no longer would I periodically have to assume the pursuer's role to keep Sarah's support money coming, but would instead depend on legally established channels.

Relief's nice. Don't expect it to last.

I took divorce papers and support order to my county courthouse and was seen by a helpful, supportive court counselor. I had assumed that it would take at least a couple of weeks for the Virginia court to process anything; had it been earlier in the day, the URESA papers would have been drawn up immediately.

URESA stands for Uniformed Reciprocal Enforcement of Support Act, which says basically that states will cooperate with each other in enforcing child support. Even a few years ago this wasn't the case: often, an absent parent simply moved to another state to avoid payment, and there wasn't much that could be done about it.

Since Sarah's case had to wait until Monday anyway, I asked the court counselor to hold the paperwork temporarily while I tried to get a current address. Once done, I called the Texas court to find out their time frame for handling incoming URESA actions. Virginia dockets petitions from other states very promptly (usually two to three weeks in Arlington County). Texas, however, generally sets a court date three to four months after receiving the paperwork from another state.

Exit all feelings of relief. Three to four months without 20 percent of our household income is a long time.

The Texas court also explained that if Sarah's dad did not pay after being ordered to, it would be up to me -- not the court -- to follow up. And if he moved to another county, the entire process would have to start all over again. One woman I spoke to recently said that her child's father had been in court five times in Florida under URESA, each time had been ordered to pay, and each time had moved to an adjacent county, effectively setting aside each court order. It appears that URESA may work on a state-to-state basis but not on a county-to-county basis.

It was remarkably easy to decide at this point to pursue the matter on my own. As much as I had wanted to step out of the frustrating, anger-provoking cycle of seeking my own enforcement, doing so would apparently be fruitless.

The more custodial parents I've spoken to about their experiences, the clearer the message: enforcement laws -- especially interstate ones -- have no real teeth.

Welfare families have state and federal enforcement systems set into action automatically, since any money collected is assigned to the state to offset welfare payments. The functions of these systems -- parent locator services, establishment of paternity and support obligations, withholding of tax refunds, wage garnishment -- technically are available to non-welfare families, too, but big gaps exist. Had I decided to use the parent locator service, it would have cost me $45 up front, with no guarantees that the "usually several months" of effort through local and national networks would net an accurate address.

A call to the Northern Virginia enforcement office revealed that it "doesn't encourage" applications for non-welfare services, and that a sliding scale fee is charged to those who do apply. Mine would be over $300.

Efforts to recoup welfare funds by placing the burden of support on the fathers of welfare children instead of on the government are both morally and fiscally sound. It can also be argued, however, that it's equally important to stress non-welfare support enforcement. Absent parents of non-welfare children are more likely to be employed, and at higher levels -- and are therefor more able to pay child support. States with mandatory wage assignment laws, such as Michigan, have collections records which appear to support this position. In FY '81, Michigan's non- welfare enforcement caseload accounted for 3 percent of that state's total, yet non-welfare collections accounted for 71 percent of the total.

Texas statistics proved quite confusing. While Texas has the third largest non-welfare enforcement caseload in the nation -- over 10 percent of the national total -- it ranks 25th in non-welfare collections. Only two states have a worse record of support collected per administrative doller spent. While the national average is $3.18, Oregon collected $9.19 per dollar spent last year. Texas collects 80 cents for each administrative dollar spent on enforcement. (The District of Columbia is worse, collecting 59 cents per dollar.)

A baffling aspect of the welfare/non-welfare issue is that, according to a local attorney, when welfare-assigned support collections reach the amount a family is receiving from welfare funds, the welfare case is closed -- and collection activities cease. This often means that support payments cease, too, and the family has to go back on welfare to start the whole cycle over. If a welfare mother knew that enforcement of the absent parent's obligation would continue, she might well see that earning her own paycheck would increase the family income beyond what welfare provides. As it is, she has more incentive to stay on welfare.

The people I've talked to in federal and state enforcement agencies, and all the court folks, generally have been helpful, knowledgeable and conscientious. The state agencies, however, are typically overburdened. The Northern Virginia state agency has 10 investigators to handle 33,000 cases. Courts can hardly be asked to go out looking for more chronic cases, which child support problems tend to be.

Given the vastness of the issue here -- at one time or another, potentially half our nation's children -- and the presence of a partly-working system, this seems the time to increase OCSE's resources, not cut them by a sixth -- $100 million -- as President Reagan has proposed.

As it is now, custodial mothers feel forced to swallow the loss of a child's support or to see partial payments as gifts rather than as half-met obligations. State and federal governments can pretty much count on us non- welfare mothers to keep our kids in shoes, but they can't go to camp or take piano lessons when their fathers don't pay.

The child support enforcement system -- especially URESA -- simply doesn't work for millions of the people it's designed to protect. According to Sen. Malcolm Wallop (R-Wyo.), the only solution is "a federal wage withholding law that is mandatory for everyone with a child support obligation and enforced consistently among the 50 states." Mary McGrory has suggested that "absent parents (fathers or mothers) may keep the child-support matter private, if they choose. All that's required is payment of the amount due, regularly and on time. Once there's a default, the process (of wage withholding) is automatic."

What seems necessary for custodial parents to understand is that as long as support money is needed, getting it is periodically going to be a major hassle.

Sarah's father has caught up the arrears which accumulated in May, June and July. There is still a sizable balance, however, of from three to six months during the previous four years. That he is still paying at all makes him above average.

Grassroots organizations of custodial parents are springing up across the country. One of the first is a Maryland group, the Organization for the Enforcement of Child Support, which provides current information on laws and related issues, and can be reached at 301- 833-2458. A northern Virginia chapter of the organization holds its first meeting in late September.

It seems to me there's an awfully large, potentially very vocal and committed group out here -- custodial parents -- to whom our legislators would do well to respond if we speak in some sort of unison. That many feet stamping at once would sure make some thunder.