Neither The New York Times nor The Wall Street Journal told New Yorkers on Jan. 5 why the corpse of Vincent Rotondo -- with a bullet through the left eye -- was found the day before with a white paper bag filled with raw fish next to it. The New York Post did. Under a headline "Waterfront Capo Shot Dead," readers were treated to the cultural and historical significance of fish as a farewell to mobsters: "The fish is an old Mafia symbol indicating the victim has been killed, thrown in the river and now 'sleeps with the fishes.' "

Such lore is among the reasons that on the mornings I can get a New York Post I'll read it before the other out-of-towns. It's a rag, but a rag that tells you stories of the city none of the other three New York dailies will. It also provides the gossip of Suzy, the joke column of Joey Adams and equally hilarious right-wing editorials that Adams probably writes during lunch.

All this may pass the way of the late Herald Tribune, World Telegram and the Mirror unless Congress restores some fairness to the media marketplace. Some unfairness occurred last month when the money-losing New York Post was made even more fragile as Sen. Edward M. Kennedy (D-Mass.) sought to take away a legal protection the paper now has. Kennedy and Sen. Ernest F. Hollings (D-S.C.) pushed an amendment that forbids the Federal Communications Commission from granting waivers to its rule disallowing ownership of both a daily newspaper and a television station in the same city.

The only owner so engaged is Rupert Murdoch. He isn't everyone's idea of journalism's Mr. Integrity. But he has kept the Post's presses running and deserves better than a waylaying by Kennedy. The senator illiberally slipped his amendment past Congress with no debate and no hearings, with a final vote coming at 2:30 a.m. If Kennedy was dreaming at that hour, it surely wasn't the result brought on by his scheme -- turning Rupert Murdoch into a champion of free speech. He's only a champion of free-speech benefits as they apply to him in the grabbing for profits.

Neither Murdoch's name nor money is linked with efforts to release journalists imprisoned in the jails of dictators. The New York Post is not known for community service. On campuses, Murdoch is a role model fit for students in the business school, not the journalism-school. The play with money, not ideas or ideals, stirs Murdoch. The high cost of press lordship in New York -- the Post loses about $10 million a year -- prompted Murdoch to be on the hunt for a buyer for the newspaper well before the Kennedy-Hollings night ride.

The effect of the legislation is to advance the Post's sale deadline. If a buyer isn't found by the end of January, say the paper's executives, operations will close by March 6. About 1,100 workers will lose their jobs. All Murdoch stands to lose is a megaphone, the one he used last week to present himself as a defenseless victim of legislative "covert action." "Nor are we the only victims," Murdoch wrote in his paper. "They include the American public, the nation's media and the integrity of Congress." Only God's honor was left out.

No quiet settlement and no friendly handshake is likely to settle any of this. The mayor of New York, as self-servingly grandiose as Murdoch, claims that the "Kennedy-Hollings measure has defamed our legislative process and undermined our freedom of the press." That's about as accurate as a New York Post headline the other day that screamed, "Soviets Already Cheating on Arms Pact." Mayor Koch knows well that the "legislative process" by which special-interest amendments are furtively attached to sure-thing bills has routinely suffered worse defamations than this latest one.

As for freedom of the press, diversity of the press is more the issue. Originally, the FCC ruled that its ban on cross-ownership was a legitimate hampering of concentrated media power. That argument has weaknesses, among them the presumption that the public is so undiscerning on the issues that it will swallow a line because it is spouted by a jointly owned newspaper and television station. A citizen wanting full access to news and opinion, whether in New York or New Ulm, won't be blocked by the local Rupert Murdoch.

New York can well survive the loss of a money-mongering publisher. Only if the Post goes down with Murdoch does the city truly lose, starting with jobs for many and diversity for everyone.