SINCE 1969, when the Supreme Court decided the case of O'Callahan v. Parker, military courts have spent time trying to decide which offenses committed by servicemen were service-related and which were not. Before O'Callahan, members of the Armed Forces could be subject to court-martial simply because of their status in the military. That case, however, narrowed the jurisdiction of military courts so that they could try only cases in which the charges were service-related.

That standard was vague and confusing, and a variety of bizarre rulings resulted. Off-post crimes against fellow servicemen, for example, were usually sent to civilian courts. But an off-post murder precipitated by something that happened on-post was held to be service-related and subject to military jurisdiction. Drug offenses went both ways.

Last week the Supreme Court took the unusual step of reversing O'Callahan and reinstating the old rule. Now the jurisdiction of a military court will again depend only on the status of the accused as a member of the Armed Forces and not on the service connection of the offense charged.

The case at issue involved a member of the Coast Guard accused of the sexual abuse of fellow guardsmen's minor daughters in a private home in Alaska during a tour of duty. The Court of Military Appeals had found some service connection in the fact that the victims were military dependents, but the Supreme Court ruled that that kind of scrambling for a link will no longer be necessary. The court reread the historical references for O'Callahan, rejected them as "far too ambiguous to justify the restriction" imposed in that case and held that the Constitution gives to Congress alone the power to make rules governing all members of the service.

Does it matter whether an accused is tried for, say, rape in a civilian or a military court? The answer is yes. Courts-martial do not proceed after grand jury indictment. A jury is not necessarily composed of the accused person's peers, and a unanimous verdict is not required. Trials can take place far from the jurisdiction where the crime was committed. Defense counsel are not always attorneys.

Dissenting justices predicted that the new ruling will "sweep an entire class of Americans beyond the reach of the Bill of Rights." If this happens, the remedy lies with Congress. The legislature can revise the military code, change procedures and incorporate new protections. If abuses occur, that will have to be done