State comptroller Yossef Shapira's report, the result of a two-year inquiry, will be published on Tuesday, a spokesman for his office said.
Shapira, who is in charge of assessing state policies and use of public funds, opened his investigation soon after the July-August 2014 conflict between Israel and Hamas, the Islamist group which controls the Gaza Strip.
A draft released to senior officials reportedly condemns Prime Minister Benjamin Netanyahu and Defence Minister Moshe Yaalon for failing to prepare for the threat posed by Hamas tunnels from Gaza, despite alerts from the intelligence services.
The report also examines "the way in which decisions were made within the (security) cabinet before and at the start of Operation Protective Edge", Shapira's spokesman said, using Israel's codename for the assault.
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The draft, released to ministers and military officials in November, says Netanyahu and Yaalon only partially informed the Jewish state's inner cabinet of the threat posed by the tunnels, according to leaks to local media.
A source close to Netanyahu has rejected the charge.
Destroying the tunnels and stopping Gaza-based Palestinian militants launching rockets into Israel were the key declared goals of Israel's third offensive in the coastal territory in six years.
Israel's military found 32 tunnels, including 14 from the Gaza Strip into Israel, according to a UN inquiry on the conflict. Hamas says it has continued to dig new ones.
The war killed 2,251 Palestinians and left 100,000 homeless, according to the UN. On the Israeli side, 74 people were killed, all but six of them soldiers.