A French factory constructing two nuclear research reactors for Iraq was heavily damaged early today when five explosive charges were set off by unknown saboteurs.

No one was hurt in the explosion, which is estimated to have set back by at least 18 months the delivery of the two reactors to Iraq, a leader of the Arab rejectionist front against Israel.

Responsibility for the explosions at La-Seyne-sur-Mer, on the Mediterranean coast, was claimed by an anonymous "French ecologist group" which said in a telephone call to a Paris newspaper that it was prompted to act by the recent nuclear power plant accident near Harrisburg, Pa.

A French government official, however, suggested that Israelis may have been involved. Responding to a query by an Israeli correspondent about the incident, the French official said, "I think you would know more about this than I do."

Israel has repeatedly protested the French-Iraqi to the French government, stressing the danger of nuclear proliferation. Israeli sources estimated that the deal, concluded in secrecy in 1975, involves more than $1 billion.

There was no indication that the police had any reliable leads on the saboteurs.

Since the Pennsylvania incident there has been widespread questioning in France of the government's announced plans to press ahead with an ambitious nuclear energy program to make up for the country's lack of natural energy resources.

But there was doubt here tonight that environment protesters have the combination of inside knowledge, sabotage skills and technical atomic information that were needed for this morning's operation.

The equipment destroyed, described as the reactors' beehive-shaped pressure vessel for atomic fuel rods, was almost finished and was to be trucked to Iraq later this month, informed local sources said.

There was no radioactive material at the site near the big French naval base at Toulon. But the contract for the controversial project is also said by informed government sources to involve the delivery of enough 93 percent enriched uranium to make about 10 Hiroshima-sized atomic explosions.

France has consistently maintained that the projected, which also includes establishment of an advanced nuclear training center for Arab scientists near Baghdad, was for civilian purposes only. French President Valery Giscard d'Estaing acknowledged publicly in an interview a year ago, however, that there was ground for concern that the uranium could be diverted to other uses.

The French are understood to have approached the Iraqis about substituting for the 93 percent weapons-grade uranium a new product they have developed, known as "caramel" involving small blocks of uramium enriched to only 3 percent, far too weak for weapons production. The first Iraqi reaction is said to have been that that was not what they had contracted for.

There is ample precedent for Israeli commando actions on French soil. Ten years ago, Israeli seamen made off with five missile-launching patrol boats built for Israel in the English Channel port of Cherbourg. Their delivery was being blocked by the French government.

The telephone statement of the daily Le Monde said, "We have succeeded in neutralizing machines that are dangerous for the existence of human life. The Harrisburg catastrophe proves once again the dangers of the atomic industry. We have gone into action and we will do whatever is necessary to safeguard from nuclear horrors the life of the French population and the human race."

Local reporters said that they were kept out of the installation, and that it was hard to see the extent of the damage, except that a portion of the 80-foot-high roof of the giant hangar had been blown through by the explosions.

Police said that five charges had gone off and that they were disarming others that had not exploded.

The atomic equipment plant, a branch of a shipbuilding company, Naval and Industrial Constructions of the Mediterranean, employs 5,600 persons. The nuclear equipment section of the shipyard and employes just 100 highly specialized technicians and engineers.

The unmarked 4,000-foot-square structure apparently did not have heavy security. There are no fences or other obvious protective measures around it, and there were only three night watchmen on duty. Until today's sabotage action, the nature of the work inside the facility was said to have been little known even to the company's other workers.

The hangar was maintained at a constant temperature for precision engineering. Those who worked inside it wore white gloves and uniforms, apparently part of an effort to minimize dust inside the installation.

In addition to the equipment for Ira, smaller reactor components destined for Belgium and West Germany were manufactured at the site.

Osirak, the larger of the two reactors being built for Iraq, is designed to produce 70 megawatts of power. It is modeled on the French nuclear research center at Saclay in the Paris region.

The deal was originally negotiated by then-prime minister Jacques Chirac and Iraqi leader Saddam Hussein.

Giscard is said by his entourage not to have understood the full implications of what Chirac had negotiated at the time. Once he did, he ordered a research program at Saclay that came up with the nonproliferating "caramel" process.Giscard has expressed concern for some time now about nuclear proliferation.