WASHINGTON — Thousands of Google employees, including dozens of senior engineers, have signed a letter protesting the company’s involvement in a Pentagon program that uses artificial intelligence to interpret video imagery and could be used to improve the targeting of drone strikes.

The letter, which is circulating inside Google and has garnered more than 3,100 signatures, reflects a culture clash between Silicon Valley and the federal government that is likely to intensify as cutting-edge artificial intelligence is increasingly employed for military purposes.

(Read the text of the letter.)

“We believe that Google should not be in the business of war,” says the letter, addressed to Sundar Pichai, the company’s chief executive. It asks that Google pull out of Project Maven, a Pentagon pilot program, and announce a policy that it will not “ever build warfare technology.”

That kind of idealistic stance, while certainly not shared by all Google employees, comes naturally to a company whose motto is “Don’t be evil,” a phrase invoked in the protest letter. But it is distinctly foreign to Washington’s massive defense industry and certainly to the Pentagon, where the defense secretary, Jim Mattis, has often said a central goal is to increase the “lethality” of the United States military.

From its early days, Google has encouraged employees to speak out on issues involving the company. It provides internal message boards and social networks where workers challenge management and one another about the company’s products and policies. Recently, the heated debate around Google’s efforts to create a more diverse work force spilled out into the open.