The Shin Bet's report was published on Tuesday, five days after the military released the result of an investigation saying it had drastically underestimated Hamas' capabilities and "failed in its mission to protect Israeli civilians".
Hamas fighters from Gaza stormed into southern Israel on October 7, 2023, killing 1200 people and taking more than 250 hostages, according to Israeli tallies.
More than 48,000 people have been killed in Israel's war on Gaza since then, according to Palestinian health officials, with the small enclave largely demolished and most of its 2.3 million people displaced, humanitarian agencies say. Around 400 Israeli soldiers have also been killed.
A fragile ceasefire has held in Gaza since January 19.
A published summary of Shin Bet's investigation said that if it "had acted differently in the years preceding the (Hamas) attack and on the night of the attack..., the massacre would have been prevented".
"This is not the standard that we expected from ourselves and the public from us," the report said.
Both investigations were published as calls grow from within the Israeli opposition and civil society for a national inquiry into the government's failures on the deadliest single day in modern Israeli history.
Soon after the start of the war, Israel's military and its main intelligence agencies admitted they had failed to foresee the lightning attack by thousands of Hamas-led gunmen.
The Israeli military's findings focused on tactical, battle and intelligence failures before, during and in the days after October 7. The armed forces chief of staff, Lieutenant General Herzi Halevi, announced his resignation in January, taking responsibility for the army's failure.
But the political establishment has so far avoided a reckoning despite repeated calls on Prime Minister Benjamin Netanyahu to hold a full national inquiry.
In a fiery parliamentary debate on Monday, Netanyahu said an inquiry would be held eventually but it must be "objective..., balanced and not dependent" on predetermined findings.
