The Federal Communications Commission - in business to protect the public's interest in our nation's airwaves - has by a 3-to-2 vote opened the floodgates to a wave of media mergers that will further crush local diversity and concentrate the power to mold public opinion in the hands of ever-fewer giant corporations.

This troubles some readers, listeners and viewers who don't like homogenized news or one-size-fits-all entertainment forced down their throats. When I inveighed against this impending sellout a couple of weeks ago, thousands - no kidding, an unprecedented torrent - of e-mails came roaring in, many beginning "Though I consider you a rightwing nutcase on most issues, I'm 100% with you against this big-media power grab."

John McCain, chairman of the Senate Commerce Committee, was also startled by the public reaction to the Floodgate scandal: "750,000 people sent messages to the F.C.C.," McCain tells me. "This sparked more interest than any issue I've ever seen that wasn't organized by a huge lobby."

Here's what happened: a single media giant, up to now allowed to own television stations reaching slightly more than a third of the nation's viewers, will soon - thanks to Floodgate - be able to reach nearly half, a giant's giant step toward 100 percent "penetration." And as for "cross-ownership" - the ability for newspapers to buy TV and radio stations in the same city and vice versa - the F.C.C. as much as said "c'mon in, local domination by a media powerhouse is fine."

Now it's up to Congress to overturn the ruling by the roundheeled F.C.C. On Thursday, Senate Commerce will mark up a bill put forward by Ted Stevens, Republican of Alaska, to roll back the penetration to 35 percent. It will be amended by Byron Dorgan, Democrat of North Dakota, to roll back the cross-ownership.

Where does Chairman McCain stand? The maverick whose hero is the trust-busting Teddy Roosevelt is uncharacteristically torn. He's against regulation in principle and admires F.C.C. Chairman Michael Powell, so he won't support Stevens's rollback to 35 percent (which McCain thinks will pass in committee, and which he won't fight) or support Dorgan's amendment on cross-ownership (which McCain thinks is doomed - "the fix is in on cross-ownership").

But I can feel the Arizonan coming around. "There's already too much concentration in radio," he says, as only four companies reach almost all listeners in the U.S. in what some of us remember as a blessedly local medium. "That could be the miners' canary. We'll hold hearings on that." (He should call in artists to examine how one radio combine gained a stranglehold on popular music.)

McCain's hesitancy means that this week's strong hand for diversity and diffusion of power is Stevens. With conservative allies like Trent Lott and Kay Bailey Hutchison joining most Democrats, Stevens has the votes for his bill. Dorgan tells me that if he cannot get a modified version of his cross-ownership rollback amendment passed, there is another way - through the Congressional Review Act - of bringing the issue to the floor.

Forgive the inside baseball (this is beginning to read like a Bob Novak column), but the legislative intricacy shows how a power grab engineered by a seemingly unstoppable lobby has at least a chance of being stymied by an aroused public resentful of media manipulation.

Media moguls slavering for massive mergers don't worry about any Senate action described above. They are sure they have Billy Tauzin, Republican of Louisiana and chairman of House Commerce, in their pocket, and think they can kill any rollback in the House.

Mebbeso, but never underestimate the political sagacity of an old Senate bull like Stevens, who doesn't get his bills passed for show. There may be some serious homeland-security angles to communications legislation that would be of interest to House conservatives and could form the basis of House-Senate cooperation.

The effect of the media's march to amalgamation on Americans' freedom of voice is too worrisome to be left to three unelected commissioners. This far-reaching political decision should be made by Congress and the White House, after extensive hearings and fair coverage by too-shy broadcasters, no-local-news cable networks and conflicted newspapers.

Listeners, viewers and readers are interested. You should see this stack of mail.