The senior official, speaking on condition of anonymity, also said Jewish settlers who ignore orders to leave by that deadline will suffer financial losses.
The official said settlers who leave before the 17 August deadline will get a better financial package, including special government grants and aid programmes that can help them re-settle.
However, he said all Jewish settlers were entitled to the same basic compensation regardless of their departure date.
17 August deadline
Before the 17 August deadline, Israeli troops will go house to house in the settlements marked for demolition and inform residents that their presence is illegal and that they must leave, the official said, confirming Israeli media reports.
Settlers who refuse to leave and are removed from Gaza will be denied special government loans or discounts available to settlers who left voluntarily before the deadline.
Prime Minister Ariel Sharon inspects
newly built settlement houses
Farming is the centrepiece of the economy in Gaza's Jewish settlements and those who leave before 17 August will be eligible to buy land at a discounted rate.
They will also be offered special loans to buy farming equipment, the official said.
Israel's government decided several weeks ago that the pullback would begin in mid-August, but Saturday was the first time an exact date was given.
Jewish settler leaders criticised the government decision and said it would be struck down by the courts.
"From every legal perspective, the government has no right to harm the residents' rights," said attorney Sarit Maoz, head of the Eli Sinai settlement council.