LIKE CRIMINAL sentences, child-support orders in the recent past have varied according to the standards of the judges as much as the characteristics of the litigants. And the complications of modern society -- which include a high divorce rate, two-career parents and obligations to multiple sets of children -- made it increasingly difficult for courts to work out sensible and fair child-support agreements.

In response to federal legislation passed two years ago, however, states are in the process of devising child-support guidelines. After two years' work, a plan was developed for the District, and on the first of this month the D.C. Superior Court began to use it.

The premise of the guidelines is that a noncustodial parent must contribute a certain percentage of gross income for the support of children. The percentage will vary according to the number and ages of the children, but the guidelines set specific contribution levels that can be easily determined. Adjustments are made that take into consideration the earnings of the custodial parent and any other child-support obligations of the parties. These factors can be weighed by formula. Suggestions are also offered for revising orders to accommodate unusual expenses and to assist the parties in coping with extraordinary responsibilities such as the care of an invalid parent. The guidelines are easy to use, and the presumption is that they will be used by Superior Court hearing commissioners, judges and parties working out their own agreements.

In divorcing families, it is not too much to ask that each parent assume an equitable share of the expenses involved in raising youngsters. Yet too often these objectives are not achieved. The children's standard of living plummets when the family breaks up, and the custodial parent is left with the lion's share of the financial burden. Devising arrangements that are fair, that sustain the children and allow both parents a decent standard of living, is a complicated task that has now been made easier. Judge Ricardo Urbino of the D.C. Superior Court and his committee of judges, lawyers and community representatives have done a good job