The Supreme Court of the United States concedes, readily enough, that the avoidance of "corruption" is a legitimate reason for Congress to regulate the use of money in campaigns. It just doesn't like the way Congress is doing it.

So this week the Court struck down a limitation on "independent" political action committee (PAC) support of presidential candidates in the name of free speech.

Justice William Rehnquist put it this way: "Allowing the presentation of views while forbidding the expenditure of more than $1,000 to present them is much like allowing a speaker in a public hall to express his views while denying him the use of an amplifying system."

The justice did well to hedge the analogy with that qualifying phrase "much like"; for the analogy is speThe free-speech clause of the First Amendment guarantees everyone the right to speak, unmolested by government. It guarantees no one an ancillary "right" to make himself heard in any given din by amplification or otherwise.

The court's logic is not only specious, it involves gratuitous meddling. Congressional restrictions on campaign expenditures deprive no one, in fact, of any right of speech. They do only what they claim to do -- they regulate the ways in which money may be spent in pursuit of public office or a political program.

Yet on the basis of this wobbly logic, the court continues to build a novel doctrine of "commercial" free speech, with implications that go far beyond politics. Who indeed will next be freed in the name of free speech from the cruel yoke of congressional regulation? Merchandisers of beef? Chicken farmers? Manufacturers of over-the- counter drugs? Stockbrokers?

And what would Madison and the other framers of the First Amendment make of this weird twisting of free- speech doctrine? In their time it was assumed, almost universally, that the goal of political discussion was the discovery of truth -- that from the din of argument truth would somehow emerge. "Whoever," asked their patron spirit, John Milton, "knew truth put to flight in a free and open encounter?"

We have, the modern age would sadly reply. We have seen truth put to flight, and disgraceful flight at that, in just the kind of big-money political extravaganzas the court now says Congress has no power to regulate.

The National Conservative Political Action Committee, a respondent in this week's case, illustrates the problem. To hear its directors tell it, NCPAC is an "informational" body. It chooses favorite candidates (it chose President Reagan in 1984) and raises and spends money to spread the good word about their virtues and views. Then, generously assisted by this pro bono service, the voters deliberate and decide.

Piou piffle.

NCPAC, and most PACs of all ideological flavors, are in essence advertisers, political hucksters, persuaders dedicated to the dissemination of sometimes not very savory distortion and propaganda.

As advertisers they should enjoy all the privileges of advertisers but no more. The regulation of advertising in the public interest has never before been considered a violation of free speech per se. As even Justice Rehnquist conceded in a lucid moment, PACs are not "lone pamphleteers or street-corner orators." So why treat them that way? And why, in the name of new-minted First Amendment values, rip to shreds a congressional scheme for regulating the flow of money in presidential politics?

That the court is in fact committing this mayhem against the Federal Elections Act and the powers of its regulatory commission, doesn't necessarily make the system a good one; and in some ways it isn't. Ironically, the present regulatory system sprang from Watergate, a scandal that had far less to do with money corruption than with abused and unaccountable power.

It is too readily assumed that the primary danger of "corruption" in politics is that the voters, or voices, of public servants might be auctioned to the highest bidder. That's always a danger, but it is probably overshadowed today by the danger that massive, promiscuous flows of special-interest money will turn campaigns into shrill irrelevancies, and the ensuing exercise of office, once gained, into baffling and unaccountable performances that spread cynicism through the public.

That is the danger the court is promoting by confusing political hucksterism with free speech.