"If orders had been followed, the terrorist act could have been prevented," Alexander Torshin, head of the inquiry into the tragedy, told lawmakers as he outlined preliminary conclusions from the investigation.
Local "authorities showed indifference and negligence in carrying out operations to prevent terrorist acts," said Mr Torshin, who is deputy speaker of the parliament's upper house.
Mr Torshin also acknowledged deficiencies in authorities' handling of the crisis, saying the "list of failures and shortcomings is long," a fact which showed that "the current system of counterterrorism measures... is not sufficiently effective."
The crisis erupted when a group of guerrillas supporting the Chechen rebel cause seized a school in Beslan, close to the border with war-torn Chechnya, taking more than 1,000 children, parents and teachers hostage.
The standoff ended in chaos and bloodshed three days later after a fierce firefight between security forces and dozens of hostage-takers killed 331 people including 186 children.
Police in the southern Russian province of North Ossetia, where Beslan is located, ignored federal interior ministry orders to tighten security around schools ahead of September 1 for the start of the academic year, Mr Torshin said.
Security chief sacked
The former FSB security service head for North Ossetia, Valery Andreyev, who headed a centre handling the September 1-3 crisis, was also "responsible for weak coordination" of Russian forces during the siege, Mr Torshin added.
Mr Andreyev was sacked within weeks of the tragedy but victims' relatives say other senior officials responsible for what they consider incompetence and the excessive use of force remain in charge.
Mr Torshin, whose inquiry carries no legal powers, spoke a day after prosecutors exonerated security officials handling the crisis of any blame.
"The expert analysis did not find mistakes in the actions of members of the crisis centre," which included army officers, secret service agents, Kremlin consultants and local officials, Deputy Prosecutor-General Nikolai Shepel said.
Mr Shepel's comments provoked angry reactions from victims' relatives, who earlier met President Vladimir Putin to outline their complaints.
Committee not objective
"We believe the work of this committee was not objective... The main aim was to cover up for top officials," Susanna Dudiyeva, head of the Beslan Mothers victim support group, said.
Marina Litvinovich, a campaigner who runs a website called Beslan Truth, told Moscow Echo radio Wednesday that Torshin's report "does not at all reveal the truth on key questions that could shed light on the events in Beslan."
The head of another support group called Voice of Beslan, Ella Kesayeva, was quoted as saying that the report was not objective, failed to name senior security officials and did not carry sufficient weight.
Launched in late September 2004, Mr Torshin's inquiry questioned 48 federal officials and 500 inhabitants of North Ossetia and will present its final report in April, commission members said.
A separate, hard-hitting inquiry by North Ossetia's assembly, which reported earlier this year, blamed the FSB security service, the interior ministry and the emergency situations ministry for failing to protect the lives of hostages.
Three police officers from Beslan are set to stand trial next month for criminal negligence in failing to stop the gunmen from entering North Ossetia and face up to seven years in prison.