President Carter was so concerned about Iraq's approach to nuclear power that he asked France in secret three times last year to tighten safeguards on the Osirak reactor it was building for Iraq. Israeli warplanes destroyed the reactor June 8.

One matter that worried Carter was Iraq's contract with Italy for a "hot cell" laboratory that could be used to extract radioisotopes from the reactor's spent fuel. Some of the radioisotopes are used to diagnose and treat diseases, but one of the isotopes is plutonium, the main ingredient of an atomic bomb.

Carter also was concerned about Iraq's attempt to purchase from West Germany, Canada and the United States 10 tons of depleted uranium fuel that could be used to make more plutonium.

What Carter won from the French in three extraordinary approaches to former French president Valery Giscard d'Estaing was an agreement to pre-irradiate the highly enriched uranium fuel so it would be "poisoned," making it more difficult for Iraq to divert it from research to an atomic weapon.

Carter also persuaded Giscard to sign a contract with Iraq that called for the presence of 150 French technicians at the Osirak reactor near Baghdad until at least 1989 to ensure that Iraq did not develop a bomb.

"Both these agreements were unique in the world of nuclear power," a source close to the Carter Administration said."They would not have happened except for Carter's intervention."

Sources close to Carter said the former president was not informed of any Israeli plan to attack the reactor if Iraq pressed on with its construction and start-up. Said one Carter source: "It's not an unlikely speculation that Israel warned Iraq of their plan but as far as I know we were never told anything in advance of what Israel was thinking."

In addition to asking France to tighten safeguards, sources said Carter also asked Italy to reconsider its sale to Iraq of a shielded "hot cell" that could be used to remove radioactive isotopes from the reactor's spent fuel.

A hot cell usually is used to extract isotopes like radioactive cobalt, which is used to treat cancer. But it can also be used to remove traces of plutonium, the preferred material for atomic weapons.

Carter was not able to persuade the Italians to stop the sale, sources said, but he did convince Italy to place a team of technicians at the Osirak site to make sure Iraq did not remove plutonium from spent fuel. There were an estimated 20 Italian technicians on duty the day before Israel attacked the reactor.

As Carter administration sources describe last summer's events, the former president was deeply disturbed when he heard that Iraq had tried to buy 10 tons of depleted uranium fuel from West Germany.

The sale didn't go through, in part because Canada squelched the deal before the United States was consulted. Canada balked because there appeared to be no good reason Iraq would want depleted uranium, except to irradiate it to make plutonium for an atomic weapon.

"You can argue that you'd use depleted uranium as a shielding material or as a training material for technicians learning to handle radioactive materials, but it's a very weak argument," one source said. "At the time, it sounded like an even weaker argument for Iraq to want to buy the stuff."

Although not rich enough in the isotope of uranium (U-235) to produce power or make a bomb, depleted uranium contains the isotope U-238, which is present in natural uranium and generates plutonium when it is bombarded with neutrons.

When U-238 absorbs a striking neutron, it turns into U-239, which then decays into the isotope of plutonium known as Pu-239, considered the best metal for making a nuclear weapon.

Depleted uranium could be formed into rods and placed in a research reactor like Osirak, then removed after absorbing neutrons given off by the fissioning uranium and reprocessed in the hot cell for plutonium.

The ony guarantee against plutonium extraction would be instruments in the reaactor that would tell inspectors the fuel had been misused.

Said one source: "If Iraq had spiked any depleted uranium with neutrons in the reactor, they would have tipped their hands completely. It would be the same tip of their hands if they had asked the 150 French technicians to leave the site so they could divert the fuel to weapons use.