It was the most explicit assessment yet of how the government sees events unfolding in the aftermath of an Israeli attack.
Matan Vilnai, who is stepping down as the "home front" Cabinet minister to become Israel's ambassador to China, described the scenarios to Israel's Maariv daily at a time of heightened debate about the Iranian nuclear threat.
Vilnai, a retired general who was deputy military chief of staff, has spent the past five years overseeing upgrades of Israel's civil defense systems, including air-raid sirens, bomb shelters and a public alert system.
In the Maariv interview, Vilnai said "the home front is ready as never before." Nonetheless, he said the country must be braced for heavy casualties in the case of conflict with Iran.
Vilnai said the government has prepared for the possibility of hundreds of rockets and missiles falling on Israeli population centers each day, with the expectation of 500 deaths.
"It could be that there will be fewer fatalities, but it could be there will be more. That is the scenario that we are preparing for according to the best experts," he said. "The assessments are for a war that will last 30 days on a number of fronts."
Israel is convinced that archenemy Iran is trying to build nuclear weapons, dismissing Tehran's claims that its nuclear program is for civilian purposes.
In his latest pronouncement, Iranian Supreme leader Ali Khamenei said Israel will disappear from "the scene of geography." Addressing war veterans in Tehran on Wednesday, he said Iran considers it its "religious duty to save this Islamic country (Palestine) from the clutches of the Zionist occupiers."
Israel's leaders have indicated an attack is a possibility if they conclude the international community has failed to halt the Iranian nuclear program.
Vilnai did not elaborate on how he reached his assessments, but his office relies on intelligence and other assessments about Iranian weapons capabilities and Israeli susceptibility. Defense Minister Ehud Barak has also said the Israeli death toll could be in the range of 500 in such a conflict.
"Just as the citizens of Japan have to realize that they can have earthquakes, so the citizens of Israel have to realize that if they live here, they have to be prepared to expect missiles on the home front," Vilnai said. "It's not pleasant for the home front, but decisions have to be made, and we have to be ready."
Vilnai has made similar comments in other media outlets in recent days.
At a news briefing in Washington on Tuesday, U.S. Defense Secretary Leon Panetta reaffirmed the U.S. assessment that Israel has not yet decided whether to strike, while the U.S. military chief, Gen. Martin Dempsey, echoed a widely held assessment that an Israeli operation would only set back, not destroy, Iran's nuclear project.
Vilnai was stepping down Wednesday to take up his new post in China. He is being replaced by a former internal security service chief, Avi Dichter.
Associated Press writer Ali Akbar Dareini contributed from Tehran, Iran.