The Senate unanimously voted Thursday to block a key media ownership rule from the Federal Communications Commission, defying a veto threat from the White House.

The rarely invoked procedural motion is an attempt to stop changes in the media ownership rules, approved by the FCC last year, from taking effect.

A similar resolution is pending in the House, but House sponsors likely don't have the two-thirds support needed to override a veto. Proponents say the measure should be sent to President Bush even if his veto allows the FCC rule to go into effect.

Sen. Byron Dorgan, D-N.D., has led the charge against the FCC's rule, arguing that it makes it easier for large media conglomerates to buy up smaller operations. "We've seen a galloping concentration in every area of the media," he said. "The same major TV channels are owned by the same companies."

The White House budget office said Thursday that it "strongly opposes" the measure and would recommend that Bush reject it if it reaches his desk.

The resolution was considered under special rules that don't allow opponents to offer amendments or block it in other ways.

Dorgan acknowledged in an interview with Dow Jones Newswires that the voice vote doesn't signal that all senators support the resolution. Asked whether there is support to override the measure, he said, "Probably not."

A Senate GOP aide said Republicans agreed to allow the measure to pass because they didn't have the ability to block under the expedited rules.

On the Senate floor, Sens. Saxby Chambliss, R-Ga., Johnny Isakson, R-Ga., both indicted their opposition to the resolution.

FCC Chairman Kevin Martin faced criticism last year when he announced his plans for reform of the media ownership rules, which haven't had any significant changes in more than 20 years. Although he lifted restrictions on only one rule - preventing a single company from owning both a newspaper and a radio or TV station in the same market - critics claimed his actions would lead to a sharp decline in the number of independent media voices across the U.S.

Martin's plan was approved by a majority of the five FCC commissioners along party lines. It would allow so-called cross-media ownership in the 20 largest media markets, assuming certain criteria were met. It would also allow companies outside the 20 largest markets to appeal directly to the FCC to allow such a transaction to take place.