THE PARENTS and relatives of 35 Americans in Bolivian prisons have just completed another in a series of visits to Washington, seeking the assistance of the U.S. government in cutting through the tangle of the Bolivian criminal justice system. The principal complaint is that the young people, charged with various drug offenses, have not been sentenced, even though some have been in prison since the spring of 1974.

On one of their earlier visits to Washington, the parents succeeded in persuading the State Department to send a study mission to La Paz to gather first-hand information on the legal plight of the Americans. One of the reasons the State Department acceded to that request is that the laws under which the Americans (and 300 Bolivians) are being held were drafted with the assistance of the U.S. Department of Justice in the early 1970s.

The core of the parents' complaint is that the United States, when it was far more exercised by the drug problem than it is today, helped create a legal quagmire in which these young people remain trapped long after our heated concern abated. Bolivia, they further point out, had no such drug laws before the U.S. Justice Department came along and helped write them. When the State Department delegation returned, it added a little weight to the parents' argument by saying that some of the cases would not meet American standards for conviction and incarceration.

Bolivia tells a different story about these young people. It maintains that it holds no innocent bystanders. Instead, the Bolivian government says, all 35 of these young Americans had some involvement with Bolivia's growing illicit cocaine market, and a few may have been dealing in heroin as well. One American was caught with 50 pounds of cocaine. He has been sentenced to 20 years in prison. There are people in the U.S. government who claim that some among the 35 had close connections with international smuggling operations and were operating in Bolivia as "mules" - i.e., couriers - for those operations.

The Bolivian government implicitly concedes that its justice has not been speedy. Only two judges have been available to handle hundreds of drug cases. Moreover, the Bolivians concede that the courts there have been reluctant to impose the harsh sentences called for under the U.S.-assisted laws. Bolivia says it plans to add more judges to process the cases, and it has already modified the sentence structure of the drug laws. What the Bolivian government does not concede is that its drug laws were written at the sole instigation of the United States. La Paz, they say, had recognized that the cocaine traffic required action before our Justice Department came along. More important, say the Bolivians, Americans cannot assume that they can get involved with drugs in Bolivia and then hope for relief from the United States should they be caught.

For all that, there are things both governments can do that would be humane and that would not infringe on either nation's sovereignty. It would be a relief to the families of the 35 Americans if they could know that their cases had been finally adjudicated. Those who are convicted would then know just how long they could expect to be in prison in Bolivia.

The single most important thing the United States can do is to make certain its citizens understand the consequences of being caught with drugs in some countries. We should also straighten out the signals we are sending abroad concerning drugs. In our own country, we are moving toward decriminalizing the possession of some substances for which the courts once gave long sentences. We very much need a clear and unambiguous drug policy, one that will be understandable to Americans and foreign governments alike.