Prime Minister Laurent Fabius tonight blamed the sabotage of a Greenpeace protest ship and a subsequent cover-up by French authorities on the former defense minister and the former head of the secret services.

The prime minister's television statement marked the first time the French government has publicly addressed the question of who ordered the sinking of the Rainbow Warrior in the New Zealand port of Auckland July 10. The government admitted Sunday that agents of the General Directorate for External Security (DGSE), as the French secret service is known, blew up the ship to keep it from leading a protest against French nuclear testing in the South Pacific.

In his television appearance tonight, Fabius managed to combine a tone of contrition for the sabotage of the Greenpeace ship with a hint of a political counteroffensive by the government. He promised compensation for the family of a Portuguese-born photographer killed when the Rainbow Warrior was wrecked, praised the French Army for its sense of duty and insisted that France would never yield to pressure to give up nuclear tests.

The government also today named Gen. Rene Imbot, 60, a battle-hardened veteran of the French Foreign Legion and the World War II resistance, as the new chief of the DGSE.

The "Greenpeace affair" has caused a political sensation in France, undermining the position of Socialist President Francois Mitterrand just six months before crucial legislative elections. It has also provoked strains between the government and the DGSE, which is a branch of the Defense Ministry.

Fabius said that, in an attempt to find out who ordered the sinking of the Greenpeace ship, he had summoned former defense minister Charles Hernu and the former head of the DGSE, Adm. Pierre Lacoste, to his office this afternoon and made each answer a series of questions.

"My conviction is that both of them acted against Greenpeace motivated by the idea that what they were doing was in the interests of our country. It is my conviction that responsibility for the Greenpeace affair and subsequent cover-up is situated at this level. But the decision was a bad one and its unfortunate execution has had serious consequences," he said.

Hernu, 62, resigned last Friday after acknowledging that there had been a cover-up at the Defense Ministry. Lacoste, 61, was dismissed for refusing to reveal the identities of French agents in New Zealand.

Suggesting that Hernu was the prime culprit, Fabius added: "In a democracy like ours, the responsibility for this kind of decision is assumed by the political authority -- that is to say, the minister."

Political analysts said that, by apportioning the blame in the way he did, Fabius appeared to be seeking to satisfy conflicting pressures from the military, the press and public opinion. Earlier in the week, sympathetic press leaks suggested that Lacoste was ready to make disclosures damaging to the government if either the military or the secret services was discredited.

The naming of another military man to head the DGSE was seen as a further step toward appeasing the military, which has traditionally been mistrustful of the Socialists.

Lacoste's successor, Imbot, is known as a tough disciplinarian and carried out a major reorganization of the Army in his previous post as Army chief of staff. The reorganization, which was opposed by some more traditional Army officers, included the creation of a 45,000-man rapid deployment force.

Asked why it had taken more than two months to establish that French agents sunk the Rainbow Warrior, Fabius said that the truth about the affair had been hidden from himself, Mitterrand and a special government investigator, Bernard Tricot.

Fabius said that it was not until Saturday that he had learned that the Greenpeace boat had been sunk by French agents acting under orders. He suggested that Hernu had lied to him by replying "no" to direct questions about whether French agents had been involved in the sinking.

"You will notice that it is since the admiral Lacoste was relieved of his functions and the minister Hernu resigned that the truth has advanced in large steps," he said.

Both Hernu and Lacoste repeatedly denied that the Rainbow Warrior had been sabotaged by French agents. Hernu has insisted for two months that his instructions to the DGSE were limited to approving an increase in information gathering against Greenpeace.

It remains to be seen whether the designation of Hernu as the principal culprit will satisfy the right-wing opposition and the press, which already has published a steady stream of revelations about the affair. Initial reactions suggested that the prime minister's statement was being greeted with skepticism.

"The lies continue," commented Michel Noir, a neo-Gaullist deputy. "Laurent Fabius knew all about this and he has denied it. That is not very courageous."