WASHINGTON — Federal regulators appear to share one view about so-called net neutrality: It is a good thing.

But defining net neutrality? That is where things get messy.

On Thursday, the Federal Communications Commission voted 3-2 to open for public debate new rules meant to guarantee an open Internet. Before the plan becomes final, though, the chairman of the commission, Tom Wheeler, will need to convince his colleagues and an array of powerful lobbying groups that the plan follows the principle of net neutrality, the idea that all content running through the Internet’s pipes is treated equally.

While the rules are meant to prevent Internet providers from knowingly slowing data, they would allow content providers to pay for a guaranteed fast lane of service. Some opponents of the plan, those considered net neutrality purists, argue that allowing some content to be sent along a fast lane would essentially discriminate against other content.

“We are dedicated to protecting and preserving an open Internet,” Mr. Wheeler said immediately before the commission vote. “What we’re dealing with today is a proposal, not a final rule. We are asking for specific comment on different approaches to accomplish the same goal, an open Internet.”