Washington ? The House voted Wednesday to prevent federal regulators from letting individual broadcast companies own television stations serving nearly half the national TV market, ignoring the preferences of its own Republican leaders and a Bush administration veto threat.

By a 400-21 vote, lawmakers approved a spending bill with language blocking a Federal Communications Commission decision to let companies own TV stations serving up to 45 percent of the country’s viewers. The current ceiling is 35 percent.

Despite GOP control of the White House, Congress and the FCC, the House vote set the stage for what may ultimately be an unraveling of a regulatory policy that the party strongly favors. The fight now moves to the Senate, where several lawmakers of both parties want to include a similar provision in their version of the bill.

Top Republicans are hoping that, with leverage from the threat of a first-ever veto by President Bush, the final House-Senate compromise bill later this year will drop the provision thwarting the FCC.

In a show of defiance, FCC Chairman Michael Powell issued a written statement before the vote defending the commission’s decision. The five-member FCC approved the new rules on a 3-2 party-line vote on June 2.

“We are confident in our decision,” Powell said. “We created enforceable rules that reflect the realities of today’s media marketplace. The rules will benefit Americans by protecting localism, competition and diversity.”

A statement by NBC lobbyist Bob Okun praised the FCC decision as “a positive and much needed step offering regulatory relief to free, over-the-air television,” and called the legislation “extremely disappointing to us.”

Rep. David Obey, D-Wis., chief sponsor of the provision that would derail the liberalized FCC rules, acknowledged in an interview that a tough fight lay ahead over keeping the language intact in the bill’s final version. But he declared victory, for now.

“It’s extremely rare to be able to reverse a regulatory decision that gives away the store to the big boys,” Obey said.

With programming power and many billions of dollars at stake, the battle has pitted the big broadcast networks against smaller station owners and an array of groups, from the Christian Coalition to the Consumers Union.

“We’ve been facing a total roadblock on doing anything in the House,” said Gene Kimmelman, public policy director for the consumer union. He said the House vote meant “that roadblock will be torn apart.”

The biggest beneficiaries of the FCC ruling would be Viacom Inc., which owns the CBS and UPN networks, and News Corp., owner of Fox. Due to mergers and acquisitions, both already exceed the 35 percent limit.

Opponents of the FCC decision said it would give giant broadcast corporations too much clout, at the expense of communities and a diversity of voices.

Supporters of the FCC rule said the older, tighter limits ignore a high-tech era in which cable and satellite TV, plus the Internet, have intensified the competition they face. And they said that with even the largest networks owning less than 3 percent of the nation’s 1,300 broadcast stations, the clout of the networks was being exaggerated.

Even so, short of support and eager to prevent FCC opponents from using a House roll call to show their strength, GOP leaders didn’t even try removing the language from the bill. Instead, they said they would seek to kill it when House-Senate bargainers craft a compromise bill later this year.

Hoping to increase their power, some Republicans were seeking House members’ signatures for a letter pledging to vote to sustain a veto, GOP aides said. It would take 145 lawmakers, or one-third of the House, to uphold a veto, which would be President Bush’s first.

Some senators may try including similar language in the Senate version of the bill, which may not be written until the fall.

The provision was included last week in a $37.9 billion measure financing the departments of Commerce, State and Justice next year.

On Tuesday, a White House budget office statement said the new FCC rules “more accurately reflect the changing media landscape and the current state of network station ownership, while still guarding against undue concentration in the marketplace.”

The budget office threatened a veto if “this provision or a provision like it with respect to any one of the other FCC rules” is sent to Bush.

On a different issue, lawmakers rejected another amendment by 273-152 that would bar the federal government from interfering with 10 states that allow the medical use of marijuana.

On Tuesday, the House by 309-118 included another amendment blocking the government from performing “sneak and peek” searches under the USA Patriot Act. That law, enacted after the terrorist attacks of Sept. 11, 2001, allowed such searches without the property owner’s or resident’s knowledge with warrants that are delivered afterward.

The House bill affected only part of the FCC’s decision.

By 254-174, the chamber rejected an amendment by Rep. Maurice Hinchey, D-N.Y., to kill the entire FCC ruling, which he said would impede local media control. The June 2 ruling also would make it easier for companies to own newspapers and broadcast stations in the same community, and to own more than one broadcast outlet in a market.