WASHINGTON — Consumers could end up the losers in a high-stakes battle among regulators, broadband providers and online entertainment giants over access to the Internet’s fastest speeds.

Thursday’s proposal from the head of the Federal Communications Commission (FCC) would allow network owners such as AT&T to levy extra charges on Netflix and other video purveyors for speedier delivery of content.

Those costs, consumer advocates said, ultimately would land on consumers’ monthly bills. The hotly debated changes also could push smaller video content providers out of business, driving up costs for those services as well, the advocates warned.

“It could create a tiered Internet where consumers either pay more for content and speed, or get left behind with fewer choices,” warned Delara Derakhshani, policy counsel for Consumers Union.

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It would be a major victory for the network providers, which spend billions of dollars a year maintaining and upgrading their networks. They long have argued that companies consuming the most bandwidth — usually with video streams — should pay extra for that privilege.

The content providers have countered that equal access is necessary to maintain a level playing field in an exploding marketplace for streaming video.

“The proposed approach is the fastest lane to punish consumers and Internet innovators,” video streaming company Netflix said Thursday. The plan would be particularly bad for smaller businesses and their customers, said Patrick Clinger, founder and chief executive of ProBoards, an online forum service.

“If smaller companies can’t afford the faster lane, they won’t be able to compete with larger companies,” he said. “Customers of smaller companies would have a lower quality experience, and that could cost companies more business.”

FCC Chairman Tom Wheeler sharply defended his plan Thursday, signaling the start of an intense debate likely to roil the industry in the coming months.

He pointed out that federal courts already have tossed out the FCC’s Net neutrality rules twice — most recently in January — so consumers are already unprotected from the vagaries of broadband providers and Internet companies. The agency, he said, needed to revise its approach or risk another reversal by the courts.

He said his plan would not allow Internet service providers or online companies to abuse consumers or small entrepreneurs.

“To be very direct, the proposal would establish that behavior harmful to consumers or competition by limiting the openness of the Internet will not be permitted,” Wheeler wrote in a blog post Thursday. His said his plan would prohibit network owners from blocking legal content and require them to provide a baseline level of service to subscribers.

The FCC also would make broadband providers act in a “commercially reasonable manner” to avoid any harm to consumers. And any deals for faster content delivery would be subject to FCC review.

The agency, for instance, could allow a faster connection that would allow a doctor to check information from a heart monitor on a patient being treated at home, said an agency official, who spoke on condition of anonymity because details of the proposal have not been made public.

The FCC has released only an outline of Wheeler’s plan. A detailed version was circulated to the FCC’s four other commissioners Thursday. It is expected to be released publicly May 15, when the members are scheduled to vote on starting the rule-making process and soliciting comments from consumers and businesses.

Wheeler, a Democrat, is open to even tougher rules for Internet traffic, such as putting broadband providers in the same highly regulated category as telephone companies, the FCC official said.

Many Democrats have advocated such a move. President Obama was a strong initial supporter of the concept that the government should make sure Internet service providers don’t act as gatekeepers of legal content.

But consumer advocates and public interest groups have lambasted Wheeler’s proposal. And that could make it difficult for him to get the votes of his fellow Democrats on the FCC.

Net neutrality is strongly supported by liberals, and Democratic lawmakers said they would be watching closely to make sure the rules aren’t weak. Republicans strongly oppose any Net neutrality rules, arguing the Internet has flourished because it has been mostly free of government regulation.