Google, Facebook, Apple and other tech companies have been moving to encrypt customers’ communications so that the government cannot monitor them without going directly to the customer. The companies’ efforts have been criticized by some in law enforcement who argue the toughened encryption will stymie their investigations.

The White House is weighing a proposal in which parts of the key to unlock digital encryption would be held by the government, and part would be held by the companies. That system was articulated by Michael S. Rogers, director of the National Security Agency, in a recent speech at Princeton University. He called for a compromise in the form of “key escrow,” where the government would hold onto part of the encryption key and companies would hold onto the other, and it would be secured with “multiple locks — big locks.”

But technologists say such a solution simply does not work. The White House’s own handpicked National Security Agency review group members, several of whom signed the letter on Tuesday, also recommended that the government support efforts to advance strong encryption.

The letter was signed by more than 140 tech companies and dozens of civil liberty, human rights and press freedom groups like the Electronic Frontier Foundation, Human Rights Watch and the Reporters Committee for Freedom of the Press. It was also signed by 60 security and policy experts including Whitfield Diffie, one of the co-inventors of the public key cryptography commonly used on the Internet today, and the former White House counterterrorism czar Richard A. Clarke, who was one of a handful of experts the White House asked to review its security policies after the revelations by Edward J. Snowden.

Apple recently switched on end-to-end encryption in its mobile operating system. Facebook turned on similar encryption in its WhatsApp messaging service. And Google has unveiled an end-to-end encryption system but has yet to turn it on as the default setting. Once it does, law enforcement will have to go directly to the user, not the companies, to read those messages.