Argentina's military government has indicated for the first time that it will provide information on the fate of thousands of people who disappeared during the military's violent campaign against leftist insurgents.

In a series of interviews and statements during the past week, high Argentine officials have revealed a plan to meet on a "case-by-case basis" with thousands of families who petitioned the government for information after relatives were seized by security forces or paramilitary squads during the late 1970s and never heard from again.

Interior Minister Alfredo Saint-Jean said the plan would lead to a "definitive solution" to the country's most divisive and internationally damaging problem. But the proposed government action appears to stop far short of the public explanations and official lists of disappeared persons that human rights groups and some political leaders have demanded.

Although few details of the proposed action have been announced, the government's statements appear to be a major departure from the firm silence of the past about the fate of the 6,000 to 15,000 persons said by local and international human rights groups to have disappeared since the military took over in a 1976 coup.

Military officials long have admitted that "excesses" were committed in the government's attempts to eliminate violent leftist groups, but have suggested that most of the persons said to have disappeared either are underground, living abroad, or were killed in confrontations between rival groups. Families seeking information have been told that the government had no knowledge of the missing persons.

The new government action apparently is designed to end years of international denunciations and a rising internal debate over the missing persons. The action comes at a time when the armed forces, led by the new president, Gen. Leopoldo Galtieri, are beginning to plan their withdrawal from the government. Negotiations began recently between military leaders and political parties on reorganization leading to a return to civilian government.

At the same time, the promises of information have been accompanied by indications that the military leaders are determined to prevent through a law or pact with the parties, the future investigation by a civilian government of the official violence.

Human rights leaders have so far reacted warily to the government's announcements while saying they will continue to insist on a full explanation of what happened to the missing persons, most of whom are now widely assumed to be dead.

"This appears to be a political operation of great scope," said Jose Federico Westerkamp, a prominent physicist and director of an Argentine human rights group. "It's not clear what will be told to the families--and it will not be enough to say that the people are dead."

"The change is that the military for the first time is talking about the disappeared," he said. "It seems that they are going to do something soon, though no one is sure what."

The country's leading newspapers and magazines began recently to run cover stories and strongly worded editorials calling for a government resolution of the issue, and high military officials--who once were said to have been sworn to a pact of secrecy on their actions--have begun making public statements in defense of the military's methods.

The change in atmosphere became obvious last month when Argentina recorded its first disappearance in over a year, a 31-year-old socialist factory worker kidnaped by men in an olive-green Ford and later found dead. The crime was covered extensively in the press and there were widespread protests by political leaders.

Government officials continue to assert that the existence of thousands of armed leftists in the country at the time of the 1976 coup necessitated a "state of war" and extreme measures.

In practice, this internal "war" came to be embodied by the sight of plainclothes agents cruising the streets of Argentina's cities in Ford Falcons with covered license plates, snatching people off street corners or from their homes without warning.

International organizations, such as Amnesty International and the Organization of American States, joined by Carter administration human rights officials, have charged that thousands of the people who disappeared in this way had no involvement in the guerrilla organizations, but were members of student, labor, or church groups suspected of leftist leanings or common citizens who were simply swept up in the massive operation.

According to rights organizations, about 6,000 cases of disappeared persons have been documented and presented to the government, and it would be in these cases that officials apparently will now offer information to families that request it.

Under Secretary of Interior Bernardo Menendez said yesterday that "in principle," the information would be given in private to each family--obviating a broad public explanation--although "this would not prevent that perhaps later the public generally would become aware" of the news.

"It seems to be a move by the government to open Pandora's box a little at a time," an editorial in the Buenos Aires Herald noted, "and thus somehow . . . lessen the international impact of the evils that may come whirling out of it."