TUCKED INTO the comprehensive criminal law reform passed by Congress in its closing days is a section directed at "protected witnesses." These are people whose testimony is needed by the government in a federal criminal trial -- usually one involving drug trafficking or organized crime -- and whose lives are endangered as a result. Since 1970, the government has been protecting these witnesses by relocating them and their families and by creating for them new identities, complete with documents and references.

Many of these witnesses were not exactly model citizens in the first place, and problems have occurred when, in their new lives, they continue to commit crimes or run out on valid financial obligations incurred before relocation. A more poignant dilemma arises when a relocated person has custody of children and the noncustodial parent is completely cut off from them. A bill introduced by Rep. Robert Kastenmeier (D-Wis.) to deal with these difficulties passed the House unanimously last spring, but the Senate never got to it. Fortunately, it was included in the big bill that Congress passed.

The new law makes the attorney general responsible for seeing that the relocated witness pays civil judgments issued against him. If the witness does not cooperate, his new identity can be revealed to the creditor or to a court-appointed guardian. Persons who are the victims of crimes committed by a relocated witness will be eligible for a special compensation program. And parents will no longer lose touch with their children because of relocation. Modification of court custody orders will be sought if necessary, and parental visits in a neutral and safe location will be arranged and paid for by the government.

More than 4,000 people have taken part in the witness protection program since its inception. That's far too many. The new law requires the attorney general to weigh a number of specific factors in deciding who needs this protection and allows him to require certain standards of participants. Only six individuals in the Justice Department will have the power to place witnesses in the program, and the new rules will provide needed structure and protections. It is a good reform that should make an important program work better.