ARLINGTON, Va. - The Internet's potential for promoting expression and empowering citizens is under threat from corporate and government policies that clash with the medium's long-standing culture of openness, some leading Internet thinkers warn.

At the annual Internet Society conference this week, the engineers who built the Internet and many of the policymakers who follow its development urged caution as governments try to exert control and businesses look to maximize profit.

``We're at a turning point in the evolution of the Internet,'' said William Drake, a fellow at the University of Maryland. A wrong turn means ``robbing it of its real democratic potential.''

Vint Cerf, co-developer of the Internet's basic communications protocols, worries that big, traditional businesses could gain unprecedented control through technical manipulation of the next-generation, high-speed services that are delivered over cable and phone lines.

Companies are inhibiting innovation, notes Cerf, by letting users receive information faster than they can send it.

``That leads to a lot of peculiar effects,'' Cerf said. Two people ``could each receive high-quality video but can't send it. They can't have high-quality video conferencing.''

Cerf is a co-founder of the Internet Society, an international, non-profit organization of Internet architects and professionals devoted to maintaining the Internet's viability and addressing issues it confronts.

With governments and businesses taking a growing interest in the Internet, the INET 2002 conference's theme was ``Internet Crossroads: Where Technology and Policy Intersect.''

The TCP/IP communications protocols that Cerf and Robert Kahn developed in the 1970s favored open standards, neutrality and flexibility over proprietary techniques, a development that later allowed personal computers to connect and innovations like the World Wide Web to develop.

That openness is increasingly threatened by ``profit motives of corporations and control issues of governments,'' said Eric Schmidt, chief executive of Google. He pointed to the current ``balkanization'' of instant messaging, where a lack of standards prevents America Online users from communicating with people on rival services.

Steve Crocker, an Internet pioneer who promoted open protocols at the standards-setting Internet Engineering Task Force, said today's decisions ``could stunt the Internet to where it becomes a mechanism for delivering entertainment, ads and conducting consumer-oriented business for large players.''

Meanwhile, proposals by some service providers to adjust access fees based on a broadband consumer's data traffic volume could inhibit the development of video and other data-intensive applications, said David Farber, a University of Pennsylvania professor and former chief technologist at the Federal Communications Commission.