PEOPLE WHO ARE confined in state institutions - prisons, mental hospitals, juvenile facilities and other such places - do not have much political clout. That may be why one of the most useful pieces of legislation introduced in this Congress has been languishing for weeks in the Senate. The bill would permit the Department of Justice to initiate lawsuits to protect the constitutional rights of the inmates of these institutions. One version of it passed the House last summer, 254 to 69, and another version, co-sponsored by Senators Birch Bayh (D-Ind.) and Orrin G. Hatch (R-Utah), was approved by the Senate Judiciary Committee, 11 to 6. But the Senate bill has yet to reach the floor because a handful of members, led by Sen. Robert B. Morgan (D-N.C.), object.

Their problem with the bill is that they, and the National Association of State Attorneys General, see it as an attack on states' rights. In one sense, it is. It would permit the attorney general to haul state agencies into federal courts. But that power is so circumscribed by the bill that it can be used in only the most egregious cases. In such cases, where state hospital or prison officials continue to abuse inmates after being told of their shortcomings, the federal government ought to be able to intervene. It does not make sense for the Department of Justice to be unable to act when it knows a particular institution is systematically depriving inmates of their federal constitutional rights.

As the law now stands, the department gets involved in lawsuits of this kind after they are filed by individual inmates. It has been asked to intervene in more than 40 cases by judges who wanted a broader investigation of the changes that had been made than an individual inmate could provide. By permitting the department to initiate cases, as well as join them later, Congress would not be opening new ways for Washington to harass the states. It would simply be helping the attorney general use his resources - and the time of the courts - more efficiently by picking its cases. In that sense, the bill is more considerate of states' rights than is the existing situation. It would require the attorney general to give the states a warning and a chance to correct deficiencies before being taken into court; an inmate does not have to give such a warning.