MIROSLAV MEDVID is the Soviet sailor who jumped ship in New Orleans. Sailors do that fairly often, and most are not allowed to stay. But because he was jumping from a Soviet ship, the possibility arose that seaman Medvid was a defector fleeing for a political reason. In those circumstances American law, official policy and public opinion afforded him special opportunity to stay. Unfortunately, the Immigration Service did not give him a reasonable chance to indicate his preference.

As it happened, in the resulting uproar over the forcible return of a struggling seaman to a Soviet ship, the State Department got into the act. It removed him from the ship, conducted overnight political and medical interviews, ascertained to its satisfaction that he wanted to go back, and marked the case closed.

What we suspect happened is that, having been returned to his ship the first time, the sailor was, if he was not drugged, then perhaps threatened in a way that made him tell the Americans on the second go-around that he was not seeking asylum. Suspecting as much, however, the Americans still could not find grounds for detaining him against his expressed will.

The way that the State Department handled the Medvid case was instantly tested in the federal courts, which declined to uphold the attempt to reclaim him for yet a third round of questioning. Legal remedies failing, some of those embracing his cause next went the political route -- to the Senate, whose Agriculture Committee issued the subpoena for Mr. Medvid that a committee aide flew off to serve yesterday. But enforcing such a subpoena is going to be extremely complicated within the confines of American law.

The appearance is that Soviet power is being exerted cruelly on a young man who has committed no known offense. It is a case bound to trouble any conscientious person. The immigration officials did damage to a vulnerable individual in the first set of interviews. It is thin consolation that American political authorities did what they could to erase that damage in the second set. Given the importance of trying to do right by this young man, the uphill effort to conduct a third set was worth making.