Eight prominent technology companies, bruised by revelations of government spying on their customers’ data and scrambling to repair the damage to their reputations, are mounting a public campaign to urge President Obama and Congress to set new limits on government surveillance.

On Monday the companies, led by Google and Microsoft, presented a plan to regulate online spying and urged the United States to lead a worldwide effort to restrict it. They accompanied it with an open letter, in the form of full-page ads in national newspapers, including The New York Times, and a website detailing their concerns.

It is the broadest and strongest effort by the companies, often archrivals, to speak with one voice to pressure the government. The tech industry, whose billionaire founders and executives are highly sought as political donors, forms a powerful interest group that is increasingly flexing its muscle in Washington.

“It’s now in their business and economic interest to protect their users’ privacy and to aggressively push for changes,” said Trevor Timm, an activist at the Electronic Frontier Foundation. “The N.S.A. mass-surveillance programs exist for a simple reason: cooperation with the tech and telecom companies. If the tech companies no longer want to cooperate, they have a lot of leverage to force significant reform.”