"He told us that war would break out at sundown, about 6 p.m.," said Nachman Shai, who was then the military affairs correspondent for Israel's public television channel and is now a Labor member of Parliament. "Forty minutes later he was handed a note and said, 'Gentlemen, the war broke out,' and he left the room."

Moments before that note arrived, according to someone else who was at that meeting, General Zeira had been carefully peeling almonds in a bowl of ice water.

The coordinated attack by Egypt and Syria, which were bent on regaining strategic territories and pride lost to Israel in the 1967 war, surprised and traumatized Israel. For months, its leaders misread the signals and wrongly assumed that Israel's enemies were not ready to attack.

Even in those final hours, when the signs were unmistakable that a conflict was imminent, Israel was misled by false intelligence about when it would start. As the country's military hurriedly called up its reserves and struggled for days to contain, then repel, the joint assault, a sense of doom spread through the country. Many feared a catastrophe.

Forty years later, Israel is again marking Yom Kippur, which falls on Saturday, the anniversary of the 1973 war according to the Hebrew calendar. This year the holy day comes in the shadow of new regional tensions and a decision by the United States to opt, at least for now, for a diplomatic agreement rather than a military strike against Syria in response to a deadly chemical weapons attack in the Damascus suburbs on Aug. 21.

Israeli newspapers and television and radio programs have been filled with recollections of the 1973 war, even as the country's leaders have insisted that the probability of any new Israeli entanglement remains low and that the population should carry on as normal. For some people here, though, the echoes of the past have stirred latent questions about the reliability of intelligence assessments and the risks of another surprise attack.

"Any Israeli with a 40-year perspective will have doubts," said Mr. Shai, who was the military's chief spokesman during the Persian Gulf War of 1991, when Israelis huddled in sealed rooms and donned gas masks, shocked once again as Iraqi Scud missiles slammed into the heart of Tel Aviv.

Coming after the euphoria of Israel's victory in the 1967 war, when six days of fighting against the Egyptian, Jordanian and Syrian Armies left Israel in control of the Sinai Peninsula, the West Bank, Gaza, East Jerusalem and the Golan Heights, the conflicts of 1973, 1991 and later years have scarred the national psyche.

But several former security officials and analysts said that while the risks now may be similar to those of past years in some respects, there are also major differences.

In 1991, for example, the United States responded to the Iraqi attack by hastily redeploying some Patriot antimissile batteries to Israel from Europe, but the batteries failed to intercept a single Iraqi Scud, tracking them instead — and following them to the ground with a thud.

Since then, Israel and the United States have invested billions of dollars in Israel's air defenses, with the Arrow, Patriot and Iron Dome systems now honed to intercept short-, medium- and longer-range rockets and missiles.

Israelis, conditioned by subsequent conflicts with Hezbollah in Lebanon and Hamas in Gaza and by numerous domestic drills, have become accustomed to the wail of sirens and the idea of rocket attacks.

But the country is less prepared for a major chemical attack, even though chemical weapons were used across its northern frontier, in Syria, less than a month ago, which led to a run on gas masks at distribution centers here. In what some people see as a new sign of government complacency at best and downright failure at worst, officials say there are enough protective kits for only 60 percent of the population, and supplies are dwindling fast.

Israeli security assessments rate the probability of any attack on Israel as low, and the chances of a chemical attack as next to zero.

In 1973, the failure of intelligence assessments about Egypt and Syria was twofold. They misjudged the countries' intentions and miscalculated their military capabilities.