MORE THAN 150 years ago, Jeremy Bentham spotted the flaw in the old judicial rule that any person charged with crime can prevent his spouse from testifying at the trial. This permits a person to convert a home into a "den of thieves," he wrote, by securing "one safe and unquestionable and ever ready accomplice for every imaginable crime." The Supreme Court, on Wednesday, spotted the same flaw. It's about time.

The "new" rule adopted by the court is that one spouse cannot prevent the other from testifying except about "confidential communications." Either spouse, however, can still refuse to give incriminating evidence against the other. That's the rule Congress enacted for the District of Columbia in 1901. The court's decision simply puts it into effect in the other federal courts.

This must have been the easiest decision the justices have had to make in years. The "spousal privilege rule" has been under attack ever since Bentham wrote and has gradualaly been eroded as its unfairness became downright oppressive. At one time, for example, it prevented a woman from testifying against her husband even if he was charged with assaulting her and their children.

The old rule was established in the days when the law regarded husband and wife as one person (male), and when no person was permitted to give evidence for or against himself in a criminal trial. The rationale for the rule evaporated more than three centuries ago when denfedants were first permitted to testify in their own behalf. But not until 1933 did the Supreme Court permit one spouse to testify for the other, and not until 1960 did it sanction testimony by a wife against a husband who had physically harmed her.

The states have their own rules. According to Chief Justice Burger's opinion, eight still forbid one spouse from testifying against the other and 16 more, including Virginia, give the spouse who is on trial a veto over any testimony from the marriage partner. Seventeen states, however, have wiped out the old privilege and permit the government to compel a spouse to testify just like any other witness.

This is a fine demonstration of the slowness with which the law has been adapted to modern views on marital and family relationships. By modern, we mean views that were modern at the turn of the century. Most of the common law governing those relationships developed when women had no rights, and some of it, like this ancient privilege, remains intact.

Justice Stewart was right in pointing out that this old privilege was no more vulnerable in 1980 than it was in 1958, when the court specifically refused to do what it did on Wednesday. The only real change has been in the justices' perception of it. Maybe that is progress.