For the next year, the Carter administration has been pressing for a law that would make it a crime to disclose the names of CIA operatives abroad, even if the information comes from musty old public documents such as the State Department's Biographic Register.

Now the U.S. Court of Appeals here has ruled that the government has been unlawfully suppressing the Register for the past six years and must make its recent editions public.

The information in the Register, a biographical rundown on more than 12,000 government employes involved in the nation's foreign policy, can be and has been used as an aid to identify U.S. intelligence officers working overseas under diplomatic cover. Since 1974, the government has treated it as thought it were stamped "Confidential," but that in fact, it has never been classified.

Instead the State Department has been refusing to make the information public solely on the grounds that its disclosure would constitute a "clearly unwarranted invasion of personal privacy."

A three-judge panel of the Court of Appeals held last week that the government's contentions to this effect were nothing more than a smoke-screen.

The lawsuit over the Register began in March 1979 after several diplomatic historians and scholarly organizations had demanded access to it under the Freedom of Information Act.

An annual publication, the Register had been available publicly from 1880 until 1974, when the Privacy Act was passed. The government suspended publication in 1975, then resumed it the next year on a much more limited basis, distributing copies only to selected federal agencies and congressional committees.

The Society for Historians of American Foreign Relations and the other plaintiffs complained that their studies had been impaired, but they were turned down on grounds of the Privacy Act and an exemption in the Freedom of Information Act applicable to "personnel and medical files and similar files" whose disclosure would be a "clearly unwarranted invasion of personal privacy."

The appellate court pointed out, however, that the great majority of employees now included in the Register had already been listed in those that were public. In addition, a survey by the American Foreign Service Associations indicated that most foreign service employes favored publication of their personal biographic information.

"When the smoke fades," the court held, "it becomes clear to us that the Register is neither a "personnel' nor 'similar' to personnel files within the meaning" of the law.

The State Department had also contended that withholding the information was proper "to protect diplomatic personnel overseas from physical harm by terrorists who could use the Register's information to justify their conduct."

The court flatly rejected the argument, and scolded the State Department for "attempting to fit a square peg in a round hole." The judges said they understood the risks of violence to foreign service personnel, but they said the personnel privacy exemption was simply not designed to deal with that problem.

"The government never invoked a national security claim," said Diane B. Cohn, a Public Citizen Litigation Group lawyer who argued the case in the Court of Appeals. She said government lawyers did file a secret memo claiming some other justification for refusing to make the Register public but it apparently failed to impress the appellate judges.

"The government claimed as evidence in the case that U.S. ambassadors in foreign countries had been attacked," she added. "We argued that you don't need the Biographic Register to know who the ambassador is."

The judges did hold one traditional item in the Register -- listing marital status and name of spouse -- could be withheld, but they ordered the release of all other information. The government has indicated that it will appeal the ruling.