France's Socialist government today sought to repair its badly damaged image in the South Pacific following its acknowledgment yesterday that French agents were responsible for the sinking of an antinuclear protest ship in New Zealand waters last July.

As the scandal widened, the French news agency Agence France-Presse, quoting reliable government sources, reported today that important secret service files on the affair had mysteriously disappeared. It said that the new defense minister, Paul Quiles, had ordered the secret services to "reconstruct" the missing evidence.

A Foreign Ministry spokesman said Prime Minister Laurent Fabius, who acknowledged French responsibility for the sinking of the Greenpeace ship, had sent a message to New Zealand Prime Minister David Lange saying he was "distressed" by the diplomatic consequences of the "Greenpeace affair." Lange has accused France of committing a "sordid act of state-backed international terrorism."

The attempt to patch up relations with New Zealand came as pressure mounted here on the French government to reveal who ordered the destruction of the Rainbow Warrior. A photographer aboard the ship was killed when it was blown apart by two underwater mines on July 10 shortly before it was to lead a flotilla of protest vessels to the French nuclear testing site of Mururoa Atoll.

The past week has witnessed the transformation of a tragicomic incident involving bungling secret agents leaving a trail of clues behind them into what the French call an affaire d'etat -- a major political controversy throwing suspicion on officials at the highest reaches of the state. At stake, according to many French analysts, is the political and moral authority of President Francois Mitterrand.

After belatedly acknowledging that the Greenpeace ship was sunk by French agents, the Socialist government now finds itself with a choice of being accused either of participation in a coverup or of incompetence in failing to control its secret services.

Signs that the "Greenpeace affair" is far from over were reflected in banner headlines in today's French newspapers, demanding to know who ordered the sinking.

"The half-confession of Fabius," and "On orders . . . From Whom?" and "Fabius: the Truth Is Cruel," were some of the headlines this morning following the prime minister's dramatic admission on live television that the Rainbow Warrior had been sunk by French agents acting "on orders."

"The affair is not finished," warned the conservative daily Le Figaro, "it is just beginning." Other papers asked why it had taken the new defense minister only one weekend to establish French involvement in the sinking of the ship while his predecessor, Charles Hernu, was unable to for two months. Hernu resigned last week after acknowledging that some of his subordinates in the Defense Ministry had hidden the truth from him. The French secret service, the General Directorate for External Security (DGSE), is a branch of the Defense Ministry.

Political analysts said that, in establishing the level of responsibility, the government had to try to satisfy conflicting pressures from the right-wing opposition, the Army, its own Socialist supporters, and the press. Opposition spokesmen have said they will not allow the military to be turned into political scapegoats.

The likely thrust of the opposition's attack became evident in a statement by Alain Madelin, a leader of the center-right Union for French Democracy party, who called the Greenpeace affair "a political scandal aimed at the demolition of the Army."

Insisting that orders to sink the Rainbow Warrior must have been given by the government, he added: "Laurent Fabius, the prime minister, Francois Mitterrand, the supreme commander of the armed forces, are in the same boat with each other."

Communist leader Georges Marchais, whose party has been most critical of the affair from the start, condemned what he called "state lies and state terrorism." He said it was difficult to believe that the "highest authorities" had not been consulted about the operation.

Socialist leaders have repeatedly denied that the government gave the order to sink the Rainbow Warrior.

In New Zealand, Lange told a news conference that the French revelations had vindicated his earlier criticism of France. But he attacked a guarantee of immunity from prosecution by the French government for the agents who blew up the ship.

"They pledged only a short time ago to bring these people to justice if it was shown that they were French," Lange said.

Last night, Fabius appeared to go back on an assurance made on Aug. 27 that any French official suspected of involvement in blowing up the Greenpeace ship would face criminal proceedings in France. Instead he suggested a parliamentary inquiry to punish those responsible for giving the orders.

France's ambassador to New Zealand, Jacques Bourgoin, today gave Lange a text of last night's statement by Fabius and an oral message from Fabius saying that he was "distressed that this affair had had consequences for relations between France and New Zealand," according to the French Foreign Ministry.

The ministry spokesman said Foreign Minister Roland Dumas would write to the family of Fernando Pereira, the photographer killed in the attack, and to David McTaggart, president of Greenpeace.