WASHINGTON-The Obama administration said Tuesday it will formally shift authority for much of the internet's governance to a nonprofit multi-stakeholder entity on Oct. 1, a move likely to spark a backlash from parts of Congress.

The administration-as well as many in the high-tech community-regard the long-planned move as necessary to maintain international support for the internet and prevent a fracturing of its governance. They say transferring authority for the internet's domain-name system to the Internet Corporation for Assigned Names and Numbers will have no practical effect on the internet's functioning or its users.

But the move is likely to stir long-smoldering concerns among some conservative Republicans, who say it could endanger national security. As recently as Friday, Sens. Ted Cruz (R., Texas) and Mike Lee (R., Utah) and Rep. Sean Duffy (R., Wis.) sent a letter to the administration, complaining again of its "planned internet giveaway."

Lawmakers have adopted budget restrictions in recent years to try to stave off the move. But existing restrictions expire Sept. 30, giving lawmakers little time to act if they want to block the Obama administration's latest executive action.

Conservative critics say the administration has been flouting the existing restrictions. Brett Schaefer of the conservative think tank Heritage Foundation on Tuesday called the National Telecommunications & Information Administration announcement "a direct violation" of the current law, which prohibits use of taxpayer funds for the transfer. He said Congress should "act to protect its constitutional authority in this matter."

Another, Berin Szoka of the conservative TechFreedom group, said "private plaintiffs could raise these issues" in court soon, even if Congress doesn't act. Some conservatives say the domain-name function could be a government asset that can't be privatized without congressional permission.

Administration officials said lawmakers have sent mixed messages on the transfer and called for government reports to Congress on its progress.

Despite the heated rhetoric, the move isn't expected to change anything for internet users for the foreseeable future, administration officials emphasized, although the change eventually could lead to consideration of new policies when it comes to tough issues such as copyright.

The administration in March 2014 announced its intent to wind down the U.S. government's stewardship role when it comes to the internet's domain-name system and relinquish control to the multi-stakeholder group, Icann, which manages a number of technical functions that help computers locate servers and websites.

In a blog post on Tuesday, the head of the National Telecommunications & Information Administration, Lawrence Strickling, said his agency had informed Icann that the government would end its role in the process on Sept. 30, by allowing the government's contract with Icann to expire. That will effectively transfer full responsibility to Icann for what some refer to as the internet's "phone book."

The transition "represents the final step in the U.S. government's longstanding commitment, supported by three [presidential] administrations, to privatize the internet's domain-name system," Mr. Strickling wrote.

The U.S. government's role "has long been a source of irritation to foreign governments," the NTIA wrote in a separate post. It has prompted some governments to call for takeover of internet operations by the United Nations or some other intergovernmental organization.

"These calls for replacing the multi-stakeholder model with a multilateral, government-run approach will only grow louder if the U.S. government fails to complete the transition," the NTIA said.

Icann told NTIA last week it had completed or would soon complete all the steps that NTIA was demanding, including measures to protect internet security.

Write to John D. McKinnon at john.mckinnon@wsj.com