WASHINGTON — Capping a yearlong debate over the principle that broadband providers should have to treat all Web traffic equally, a federal agency is expected to enact the nation’s first rules today regulating high-speed Internet providers and setting guidelines for the emerging market of video over the Web.

For consumers, the agreement is designed to ensure vigorous competition in the market to send higher-quality movies and TV over the Internet. But it opens the door to high-volume Internet users having to pay more, which could boost the price of some of that video.

The Federal Communications Commission is set to approve so-called network neutrality rules despite opposition from both ends of the political spectrum. The suspense surrounding the vote was removed Monday when the swing vote on the five-member commission, Commissioner Michael Copps, announced that he will vote for the compromise plan crafted by FCC Chairman Julius Genachowski.

A staunch net neutrality backer, Copps said in a statement that he would have drafted stiffer rules if it were up to him. But the proposal before the commission “could represent an important milestone in the ongoing struggle to safeguard the awesome opportunity-creating power of the open Internet,” he said. “While I cannot vote wholeheartedly to approve the item, I will not block it by voting against it.”

The debate has taken on urgency in recent months as consumers increasingly use their Web connections to watch movies and TV shows, a phenomenon that poses a threat to pay-TV providers such as Comcast and AT&T. The fear is that those companies will use their control over high-speed Internet lines to undercut potential online competitors like Netflix or Amazon, which offer streaming video for a fraction of the cost of a cable TV subscription.

The broadband companies could do so in a few ways: by transmitting their own video so it streams superfast and clear, while making competing Web video look slow and choppy; or by making competing online video sites pay for priority access on broadband networks, indirectly raising prices for those services.

The FCC rules are designed to protect online video providers from such anticompetitive behavior — or, as Copps put it, to put “consumers, not Big Phone and Big Cable, in maximum control of their online experiences.” High-speed Internet providers would be barred from blocking any legal website or application or from transmitting traffic over their networks in a way that discriminates against competitors. Arrangements in which websites pay for faster delivery — known as “pay for priority” — are singled out as “particularly problematic,” a senior FCC official said. Wireless Internet providers would be subject to somewhat less rigorous rules.

But the proposed rules, which have yet to be released publicly, apparently take a more agnostic view of charging Web users based on how heavily they tap broadband networks. Such tiered pricing plans — which would mean people who download a lot of YouTube or Netflix videos pay more for broadband service than those who just browse the Web — could dampen demand for online video sites. But Genachowski argued earlier this month that tiered pricing could also give broadband providers a better return on investment and entice them to upgrade their networks.

The FCC plans to monitor any tiered pricing plans to ensure that they are fair to consumers.

The FCC will consider accusations of rules violations on a case-by-case basis, looking into complaints brought to it by outside groups or initiating its own investigations. Violators could face injunctions or fines.

Genachowski’s proposal has support from several Silicon Valley venture capitalists, including John Doerr, and entrepreneurs, including Craigslist’s Craig Newmark. Big broadband companies give it tepid support, relieved that Genachowski backed off an earlier push to subject them to much stricter rules that govern phone companies.

But some legislators on the right say the new regulations for Internet providers could disrupt a thriving sector of the economy, and public interest groups on the left argue that the plan doesn’t go far enough to head off bad behavior by broadband operators.

“Instead of a rule that would protect everyone — from consumers to applications developers — from predatory practices of telephone and cable companies, the commission settled for much less,” said Gigi Sohn, president of Public Knowledge. “Instead of strong, firm rules providing clear protections, the commission created a vague and shifting landscape open to interpretation.”

Contact Mike Zapler at 202-662-8921.