The official leadership of the French Jewish community today hardened its attitude toward the government as thousands of people took part in a series of major demonstrations here to protest the bombing last night during religious services of the capital's leading Reformed synagogue.

Baron Alain de Rothschild, the titular leader of French Jewry and normally a moderate voice, denounced the "passivity of the authorities and the indifference of our rulers" toward anti-Semitic right-wing extremist groups. He dropped his previous opposition to the formation of Jewish self-defense units demanded by militants who challenge the leadership of the French Jewish establishment.

French police unions echoed Rothschild's complaint about the "inexplicable impotence" of the police against extremists of the right, in sharp contrast to their vigorous pursuit of leftist extremists.

Interior Minister Christian Bonnet has a list of 150 members of the most publicized neo-Nazi group, which includes 30 policemen, alleged Jose Delthorn, leader of the most important independent police union, at a press conference.

The police unions attacked previous statements by Bonnet minimizing the dangers from the extreme right and alleged that police intelligence has been given orders to concentrate on the extreme left and on the conventional political opposition.

The death toll in the bombing outside the synagogue in the fashionable 18th district was brought down to three after it was realized that one family had mistakenly identified a badly burned body as its relative. There were fears, however, that one of the dozen severely wounded persons would not pull through.

Referring to a statement last night by President Valery Giscard dEstaing calling on the police to conduct an "exemplary action" to find the perpetrators of the bombing, Rothschild demanded to know "what exceptional measures" the government plans to take.

It was announced that three extra companies of France's tough paramilitary riot police are being rushed to Paris to protect Jewish community buildings. Police announced the arrest on 13 rightist activists, but it was considered doubtful that charges would be brought against any of them. Police sources said that no known neo-Nazi groups or individuals are actually suspected. Arresting known activists after such incidents is a standard police tactic that rarely yields results.

Noting that antiracist movements, the police unions and the neo-fascists themselves have been proclaiming for some time a stepup in neo-Nazi activities, the influential newspaper Le Monde said in a front-page editorial by editor Jacques Fauvet that the police have been watching the wrong extremists despite a series of political assassinations and other violence that were clearly the work of neo-fascists.

Jean-Pierre Pierre-Bloch, a prominent Jewish leader, told a meeting of thousands of people by the walls surrounding the presidential palace that he had gotten a pledge that the dissolution of all neo-Nazi groups in France would be announced Wednesday after the next weekly Cabinet meeting.

Interior Minister Bonnet has been saying that the dissolution of extremist organizations is not a useful approach. But his critics point out that the government's dissolution of a number of leftist groups after the May-June 1968 student-worker rebellion succeeded in disorganizing the most violence-prone fringes of the extreme left.

Bonnet and Giscard were the butt of many of the leftist groups that joined in demonstrations outside the nearly adjoining Interior Ministry and the Elysee Palace. The most frequently heard chant seemed to be "Giscard, Bonnet -- Accomplices of the Assassins."

Simone Veil, president of the Enropean Parliament in Strasbourg and a prominent Giscardist, had to be rescued by police from a group of young Jewish militants screaming the slogan at her. A Jewish former concentration camp inmate, she told the demonstrators, "Don't behave like those you are fighting. Just disperse without forgetting."

On a beautiful Indian Summer day, the mood of a crowd of more than 10,000 that marched from the Interior Ministry, up the Champs Elysees to the bombed synagogue this afternoon seemed to vary between anger and militancy and the gaiety of a late-summer outing. The throng included practically all the antiracist, Jewish and political groups in France.

The Palestinian student union of Paris denounced the synagogue bombing and recalled that Palestinians and Arabs have often also had to suffer racist outrages in France. The Algerian workers social organization in France sent a similar message to the grand rabbi of France.

Rothschild expressed a frequently heard sentiment among Jewish spokesmen here when he said in what was clearly a criticism of France's pro-Arab foreign policy: "One should not be astonished that, after turning Israel into a scapegoat by constantly censuring it while minimizing the activities of others, to see an upsurge of anti-Semitism."