The law reduces the approval required to go to war from the full cabinet to half of the much smaller security cabinet under most circumstances. But a provision was added late in the process to give that authority to the prime minister and defense minister in “extreme circumstances.”

“The last minute addition giving authority under extreme circumstances to the prime minister and defense minister on their own appears to be out of order,” said Yehuda Ben Meir, the head of the national security and public opinion project at the Institute for National Security Studies at Tel Aviv University. “It is not appropriate to Israel’s constitutional system of government.”

The law does not define what constitutes “extreme circumstances.”

Previously, Israeli leaders had to seek the approval of the full cabinet to go to war, or even to embark on a military action that was likely to lead to war. But in recent years, governments have swelled to up to 30 ministers. Advocates of the new law say that with the larger cabinets, that system has become unwieldy.

However, some experts also said that the law may have little practical effect since the prime minister and defense minister were unlikely to go to war without strong political backing and the support of the military and security agencies, which have proven in the past to be cautious.

“A government cannot go to war, no matter what the law says, without a national consensus,” said Shlomo Avineri, professor emeritus of political science at the Hebrew University of Jerusalem.

That Mr. Netanyahu’s motives could come under suspicion because of his legal troubles only strengthens the need for public and political support, Mr. Avineri said.

“Obviously a prime minister under investigation is limited by the kind of choices he can take, and they will be scrutinized even more than usual,” Mr. Avineri said, adding that in such a case, “the necessity for broad support is even wider.”