The Department of Justice has taken the action it promised on subpoenaing the telephone records of news reporters. But there is less to it than meets the eye.

By a change in the department's regulations, the attorney general must personally approve subpoenas for reporters' telephone toll records. Under the original regulation, that was not necessary.

Twice since the days of John Mitchell, newsmen's telephone records have been turned over to the department for use in criminal investigations. That is twice, maybe. Those are the only two cases that are known.

Both became visible during the fall, before the regulation change, when the respective telephone companies, as they are required to do, notified reporters of the subpoenas. Seven months of the records of The New York Times' bureau in Atlanta and the home records of its bureau chief had been subpoenaed in June. Notification came in September.

An AT&T policy specified notification after 90 days, but that was apparently extendable indefinitely. Nine months of records of three Philadelphia Bulletin reporters were subpoenaed, and they were informed a year later. The Justice Department had held up notification.

The department has authority to take this kind of action under a 1978 decision by the U.S. Court of Appeals in Washington. It held that telephone records are the property of the telephone company, not individuals or companies. It is a bad ruling. A parallel decision would be if the court held that personal correspondence is the property of the post office.

After the decision, the Justice Department wrote implementing regulations. The department's policy says:

"Because the freedom of the press can be no broader than the freedom of reporters to investigate and report the news, the prosecutorial power of the government should not be used in such a way that it impairs a reporter's responsibility to cover as broadly as possible controversial public issues."

Under that policy and the original regulation, neither a reporter nor a reporter's notes could be subpoenaed without the personal approval of the attorney general. Telephone records were not included. Now they are.

And the consequences? "It's less than a half a loaf," in the words of Jack Landau, director of the Reporters Committee for Freedom of the Press. Mr. Landau's caution is that any subpoena for reporters' telephone records is to be issued, in the new regulation's language, with "reasonable and timely notice" to the reporter. Reasonable and timely notice is suspended, however, if the responsible assistant attorney general determines that the notice would threaten the department's investigation. Notice may be delayed 90 days, and that may be extended if past departmental interpretation is continued, as with the Bulletin's reporters.

There is another major problem. A subpoena for a reporter or reporter's notes is a neatly precise legal instrument. It seeks and gets only what it narrowly defines; that is, testimony on a single case or notes only on the investigation being prusued by the department.

A telephone records subpoena, on the other hand, is a vacuum cleaner. It sweeps up everything including not only calls to or from a banker, lover or relative but detailed information on a reporter's conversations on whatever rang of stories he or she happens to be working on. Put another way, the newly altered regulation leaves at risk any long-distance calls into or out of a newsroom or the home of a reporter. That is a significant and ominous intrusion into news gathering. It is legal, under the Court of Appeals decision, but it is far wide of the Justice Department's policy.

The altered regulation does have one virtue. By requiring the attorney general to sign personally all subpoenas for reporters' telephone records, a half-step has been taken. It makes the attorney general's approval visible, for whatever restraint that is likely to impose.