Israeli warplanes bombed and destroyed a French-built nuclear reactor near the Iraqi capital of Baghdad that posed a threat "to the very survival of Israel," the Israeli government said today.

The Army command said that the Israeli planes flying more than 600 miles across Arab territory yesterday, "completely destroyed" the uranium-powered reactor located about 12 miles southwest of Baghdad in a mission "carried out to perfection." All the Israeli planes returned to their bases, the command said.

One French technician at the reactor was killed according to an official French spokesman. There was no report of Iraqi casualties.

Although Iraqi statements on the bombing did not mention radiation danger, American nuclear experts suggested there might be more than minimal radiation damage at the Iraqi site.

The Israeli government, which had said there were no foreign casualties, said the bombing raid was scheduled for Sunday on the "assumption" that the 100 to 150 French nuclear technicians who work at the 70-megawatt reactor would be off duty.

The raid is expected to seriously complicate efforts to defuse another major Middle East dispute between Israel and Syria over the presence of Syrian antiaircraft missile in Lebanon. It was condemned by the United States, the Soviet Union and France as well as some Arab governments.

Iraq said its nuclear technology had not been seriously damaged and would quickly be rebuilt. It accused Israel of collusion with Iran, with whom the Iraqis have been at war for eight months, and asked for an immediate meeting of the U.N. Security Council.At Iraq's request, the Arab League prepared to call an urgent meeting, probably for later this week, to discuss the Israeli raid.

More than 24 hours passed from the time of the attack until the Israel announcement, without a word of protest from the Iraqi government. The State Department in Washington said it had no prior knowledge of the raid and learned of it from Israel after completion of the mission.

Prime Minister Menachem Begin said in a radio interview tonight that the decision to bomb the Iraqi facility was made "many months ago" but he had postponed repeatedly the attack day -- which Radio Israel said at one time was May 10, the day of the French election.

The air strike appeared to give Begin a significant boost in his campaign for reelection June 30, as his opposition candidates tonight issued a flurry of statements supporting the operation and echoing his concerns about the threat to Israel of an Iraqi nuclear arsenal.

Israeli officials did not say what type of planes were used for the raid or what route they took to reach the Iraqi capital, 620 miles east of Tel Aviv.

An Iraqi press agency account said only that nine planes were used and, in Washington, State Department officials said U.S.-built planes were used.

[Sources in Washington said the Israeli aircraft flew across northern Saudi Arabia, presumably refueling in midair.]

The raid was ordered, the Israeli statement said, because reliable intelligence sources had indicated that the reactor was to produce material from which nuclear bombs could be made to be used against Israel.

Israel said it decided to act now because in a few months the reactor would be operational and "hot" and that bombing it then would scatter deadly radioactivity over densely populated Baghdad.

Had Israel not acted now, the government said, "we would have been compelled to passively observe the process of the production of atomic bombs in Iraq, whose running tyrant would not hesitate to launch them against Israeli cities, the centers of its populations. Therefore, the government of Israel decided to act without further delay to insure the Israeli people's existence."

The Iraqi reactor, according to the Israelis, was nearing the capability of producing fissionable material that would allow Iraq to make atomic bombs of the size exploded over Hiroshima, Japan, near the end of World War II. It would have been operational in either early July or early September, according to Israeli intelligence.

"Thus, a mortal threat to the very existence of Israel was emerging," the Israeli government declared.

As evidence of that danger, the Israelis cited statements made by Iraqi President Saddam Hussein shortly after jets with Iranian markings bombed the reactor last Sept. 30, causing only superficial damage to auxiliary buildings.

"Saddam Hussein stressed that the Iranian attempts to attack the reactor were pointless since it was being constructed against Israel alone," the Israeli statement said.

At the time of the Iranian air strike, there were suggestions in Baghdad and abroad that Israeli aircraft disguised with Iranian markings had been responsible. Israel denied it was involved in that air strike.

In an obvious reference to France, which sold the $260 million experimental reactor to Iraq, and to Italy, which supplied a $50 million radiochemistry laboratory complex, the Israeli government today declared:

"Two European governments, in return for oil, have assisted the Iraqi tyrant in the construction of atomic weapons. We again call upon them to desist from this horrifying, inhumane deed. Under no circumstances will we allow an enemy to develop weapons of mass destruction against our people. We will defend the citizens of Israel, in time and with all the means at our disposal."

In the radio interview tonight, Begin said, "We are convinced from the information at our disposal that they could have produced there, four or five bombs . . . and Saddam Hussein is just the person who could have done it because he murdered at his own hand his political adversaries and you must understand that for the last two years I have been living in a nightmare.

"I used to see groups of little children who asked me questions and greeted me, and I knew that these children might be victims of an atomic bomb."

When asked what kind of world reaction he expected to the raid, Begin said, "We will understand all the reaction, because what we did was defend ourselves. . . . We warned the French, we told them not to continue to supply the Iraqis with this equipment."

Asked about Arab reaction, Begin replied, "I don't care about the Arab world. I care about our lives."

The U.S. Central Intelligence Agency has reported in the past that Israel has already produced nuclear weapons. In 1979, Israel was reported to have exploded in atomic device off the coast of South Africa, although it officially denied the report.

Israel has never confirmed it is engaged in developing atomic weapons at its nuclear research complex near Dimona, in the Negev desert, saying only that Israel will not be the first country in the region to introduce nuclear weapons.

The core of the Iraqi nuclear program was purchased from France after Jacques Chirac, then French prime minister, visited Baghdad and discussed with Saddam Hussein the sale of two reactors, one for power production and the other for research. The Iraqis first insisted on purchasing a 500-megawatt uranium graphite-gas reactor that could produce not only electricity but also hundreds of pounds of plutonium, which could serve military purposes.

After long negotiations, the Iraqis finally bought the 70-megawatt reactor, along with six charges of 26 pounds of uranium enriched to 93 percent -- enough weapon-grade fuel for the production of three or four nuclear devices. The French also agreed to help train 600 Iraqi technicians and scientists, and to supply a second reactor, a 1-megawatt research facility.

Iraq then committed itself to sell France 70 million barrels of oil annually and buy $1.5 billion in arms from France. The arms purchases reportedly included an integrated air defense system built around 60 Mirage F1 fighters, mobile antiaircraft missiles, radar installations and an electronic early warning system said to be worth $600 million.

From Italy, the Iraqis bought four research facilities, including a radio-chemistry laboratory equipped for reprocessing irradiated fuel elements and separating plutonium, which could be used in atomic weapons.

Israel's leading nuclear physicist, Yuval Neeman, of Tel Aviv University, said in a radio interview tonight that it was obvious from scientific conferences he has attended that Iraq, even though it signed the Nuclear Nonproliferation Treaty -- which Israel has not signed -- was preparing to build nuclear bombs.

He accused the French of irresponsibility after the Sept. 30 air attack for leaving the nuclear reactor and 26 pounds of enriched uranium in place.

Last November, Iraq prevented inspection of its nuclear facilities by the International Atomic Energy Agency, saying that the inspectors could not come to Baghdad because of the war between Iran and Iraq. Since then, it has resumed permission for inspections and one was carried out earlier this year.

Neeman said Israel would have had to use special bombs and bombing techniques to destroy the reactor, which is housed in a multistory building. He estimated that it will take Iraq three years to rebuild the facility.

Yesterday's bombing raid was not the first incident aimed at delaying Iraq's nuclear program. In April 1979, saboteurs destroyed the core of an Iraqi-bound reactor as it lay in storage in France and there were unconfirmed reports at the time that the saboteurs were Israeli agents.

Last August, a senior Egyptian-born nuclear scientist who was a principal figure in the Iraqi nuclear program was killed in his Paris hotel room and again there was speculation that Iraeli intelligence agents were responsible. Israel denied involvement in both incidents.

For more than a year, Israeli officials have raised the alarm publicly about the Iraqi nuclear development program. On July 14, 1980, France's national day, Begin made a speech in which he accused France of "creating," an extremely dangerous situation," and in a television interview the same day, Deputy Prime Minister Yigael Yadin said Israel would take measures against the atomic program.

Reaction tonight from Israel's opposition party leaders was guarded and, for the most part, supportive of the strike.

Opposition Labor Party leader Shimon Peres, vacationing in the resort city of Eilat, said, "Once again, the Israeli Air Force showed it is the best in the world."

Similar backing of the raid came from former prime minister Yitzhak Rabin and former foreign minister Abba Eban. Eban said, "The Air Force was given a great mission which it accomplished with superior talent and bravery," but he said the mission should have been conducted after the election so that the new government would face the "political consequence."