PORT-AU-PRINCE, Haiti (AP) _ Mob intimidation of the courts and legislature is causing apprehension about President Jean-Bertrand Aristide's populist brand of democracy.

''The arbitrariness of mob rule can destroy our budding democracy, which must be synonymous with the rule of law,' said Jean-Claude Bajeux, a prominent socialist.

Last Tuesday, about 1,000 activists from slum organizations laid siege to the Legislative Palace, looted and burned the offices of two dissenting groups and roughed up a lawmaker.

They threatened other legislators with the ''flaming necklace'' - death by a burning car tire around the neck - unless they stopped trying to censure Rene Preval, Aristide's prime minister. The legislators went home.

At the end of July, with blinding speed, a court tried Roger Lafontant, deposed dictator Jean-Claude Duvalier's security chief, and 21 collaborators on charges of attempting a coup in January.

Aristide, who took office in February, said he wanted justice to be swift and severe.

It was in this case: All defendants were convicted in just 24 hours and nearly all were sentenced to life at hard labor, although jurists say the maximum under law was 15 years.

Activists from the slums had threatened the judge with the flaming necklace if Lafontant, who led the Tonton Macoute terror network, and the others were not convicted.

Many Haitians were appalled and embarrassed. Jean-Jacques Honorat, a prominent human rights activist, called it ''a parody of justice, which the public saw as a shame for the Haitian judiciary and the country as a whole.''

President Aristide, a 38-year-old Roman Catholic priest, has denied any role in the mob actions or threats but has not explicitly condemned them.

A government statement Wednesday criticized the attack on the legislature only mildly, describing it as contrary to Aristide's efforts to build a peaceful society with respect for human rights.

''The fork of division cannot drink the soup of democracy,'' it said, but added that ''neither the government nor the people bears the responsibility'' for the attack.

In a speech to student activists on Aug. 4, the president defended the use of popular pressure. He said the 4-year-old constitution did not sanction the flaming necklace, but neither did it say ''the people should forget it.''

He indicated the belief that, if the judge had not been threatened, Lafontant might not have received a life sentence.

Aristide embraced liberation theology as a priest and advocated ''active non-violence.'' He helped lead a grassroots campaign against the Duvalier dynasty, which ruled this impoverished Caribbean nation for three decades.

After Jean-Claude Duvalier fled in 1986, Aristide was criticized for appearing to condone rampages in which mobs of slum-dwellers killed Duvalier collaborators and looted their homes.

Aristide toned down his rhetoric after becoming president and has pursued moderate policies, with the support of the United States and other Western countries.

He now advocates ''participatory democracy,'' encouraging citizen action through organizations of slum dwellers and peasants, which have proliferated in recent years.

Hundreds of such groups exist in Port-au-Prince and probably thousands in the countryside, ranging in size from a half a dozen members to perhaps 200. Many of the activists are influenced by Aristide's philosophy and some call him ''the prophet,'' but they often appear beyond his or anyone else's control. Confrontations between the groups and authorities occur regularly.

''The myth of direct democracy will lead to anarchy if, under Aristide's influence, groups of the urban poor continue their violent assault on the institutions of representative democracy,'' Bajeux, the socialist, said in an interview.

Jean-Claude Roy, a center-left politician and constitutional scholar, said: ''The so-called popular organizations, to which Aristide refers when he talks about participative democracy, are in fact disorganized and, insofar as they oppose constitutional norms, unpopular.''

Parliament seeks explicit recognition from Aristide's administration of its authority as an elected body over that of appointed officials and non-elected pressure groups, especially the urban militants.

In Tuesday's stormy session, Preval challenged the legislature's authority, which appears clear in the constitution, to force his resignation through a vote of no confidence.

Chamber president Ernst Pedro Casseus, said to be close to the government, adjourned the session without taking a confidence vote.