FOR TWO decades, .com, .org and some 20 other “generic top-level domain names” have served as calling cards for the vast majority of Web sites. That may change dramatically — and not for the better — if the obscure but powerful organization that manages domain names gets its way.

Starting next month, the Internet Corporation for Assigned Names and Numbers (ICANN) plans to take applications from individuals and groups interested in plunking down $185,000 a pop to buy the rights to new domain names — the words to the right of the dot. Some of these could focus on a community of businesses or services, such as .bank or .news. Others may be used to market specific brands or products, as in .Coke or .Chevy. ICANN officials say that they expect up to 500 applications to be filed between January and April when the organization opens the process; those approved would go live in 2013. ICANN believes these changes will lead to innovations that build on the already explosive growth and inventiveness of the Internet age.

Businesses, nonprofits and law enforcement officials take a dimmer view. “A potential disaster,” declared Federal Trade Commission Chairman Jon Leibowitz during a congressional hearing last week. An invitation to extortion, cried a coalition of businesses. A crippling blow, warned a group of nonprofits.

Mr. Leibowitz worries that the proliferation of names will increase the incidence of fraud; ICANN’s error-riddled database of Web site and domain name owners, he testified, already makes it difficult to track down scammers. Businesses say that they will be forced to spend millions in “defensive registrations” to prevent interlopers from claiming their brand or product names; the new addresses, they say, will duplicate existing sites and cause confusion. Nonprofits say that they cannot afford the stiff fees. Representatives from these groups aired their complaints during a Senate hearing Thursday — not that lawmakers have any power to resolve the controversy.

ICANN reports to no one — a decision made when the group was created during the Clinton administration to protect Internet independence. The group has made some adjustments in response to concerns, including creation of a trademark clearinghouse and a “rapid response” process to allow legitimate rights holders to quickly knock out imposters. Officials have said that some nonprofits may be permitted to pay lower fees.

Although the plan has been six years in the making, it is not ready for prime time. ICANN officials acknowledge that they are still working out some details, including certain protections for trademark holders. The Justice Department and other law enforcement agencies have expressed concerns about enforcement.

ICANN should not approve new names until enforcement and protection issues are resolved. Even then, it should approve at most a few, to allow the marketplace to absorb and weigh the changes. ICANN would be wise to move slowly; its legitimacy and Internet efficacy are at stake.