The Supreme Court yesterday cast aside one of the ancient privileges of marriage: the ability to prevent your spouse from testifying against you in court.

Instead, the court left each partner in marriage free to decide whether to testify against the other.

The justices ruled that lower courts acted properly when they allowed a Los Angeles woman to testify against her husband over his objections in a drug smuggling case. The man, Otis Trammel, was convicted. His wife, Elizabeth Ann, was given immunity from prosecution.

The court left untouched two other traditional marital privileges. Husbands and wives still cannot be compelled to testify against if they do not want to. And if by chance, they do testify, they may be prevented from revealing confidential marital communications.

Yesterday's unanimous ruling applies only to federal trials. Twenty six states, including Maryland, have already eliminated in their own cases the rule invalidated yesterday by the Supreme Court. So has the District of Columbia. Other states, including Virginia, still have the old rule or a variation of it, and may keep it.

The court said the old federal procedure was based on several outmoded notions. One, that a wife, as merely an extension of her husband, violated his protection against self-incrimination by testifying against him, is "ancient" and unfair, the court said.

The other, that the rule would preserve martial harmony, is simply "unpersuasive." Anytime one spouse is willing to help send the other to jail, the court observed, "there is probably little in the way of marital harmony" left to preserve anyway.

Both rationales are outweighed by the need of the criminal justice system to get at the truth, Chief Justice Warren Burger wrote for the court.

The old rule, according to Burger, was based in part on the belief that "husband and wife were one, and that since the woman had no recognized separate legal existence, the husband was that one . . . What was inadmissible from the lips of the defendant husband was also inadmissible from his wife."

These "ancient foundations," Burger wrote, "have long since disappeared. Nowhere in the common-law world -- indeed in any modern society -- is a woman regarded as chattel or demeaned by denial of a separate legal identity and the dignity associated with recognition as a whole human being.

"Chip by chip, over the years, those archaic notions have been cast aside so that "no longer is the female destined solely for the home and the rearing of the family, and only the male for the marketplace and the world of ideas." Burger wrote, quoting a 1975 decision of the court.

In thetory, the court's decision preserved the right of one spouse to object if the other starts spilling marital intimacies in the courtroom.In practice, defense lawyers noted, a large number of intimacies can come out before being drowned in a chorus of objections and cut off by a judge's ruling. b

The women's rights language, coming from a chief justice said to be self-conscious about his reputation as a conservative on women's issues, appears to prompted a cryptic byplay between Burger and Justice Potter Stewart.

Stewart, in a concurring opinion, said "there is reason to believe that today's opinion, of the court will be of greater interest to students of human psychology than to students of law."

Stewart also noted the court was overturning its 1958 decision which upheld the old rule and gave it its name, the Hawkins Rule. Suggesting the court should have acted sooner, Stewart wrote that the "ancient foundations' referred to by Burger had -- disappeared well before 1958."