NEW YORK, JAN. 7 -- The political fallout over the effort by Sen. Edward M. Kennedy (D-Mass.) that could force Rupert Murdoch to sell the New York Post escalated today as Mayor Edward I. Koch (D) and civic and labor leaders turned out to help save the newspaper and denounce the Kennedy maneuver.

At a Senate hearing in Manhattan, one local publisher charged that Koch is rallying to Murdoch's side because the Post has been the mayor's staunchest editorial ally. At the same time, Koch and others suggested that Kennedy's actions are motivated by a strong dislike for the Post that dates to Kennedy's 1980 presidential campaign.

The conflicting charges involve a rider that Kennedy quietly inserted in the omnibus congressional spending bill last month that could force Murdoch to sell the sensational, money-losing Post by March 6 in order to retain WNYW-TV, Channel 5, his television station here.

Murdoch could also be forced to sell either the Boston Herald, which frequently criticizes Kennedy, or Boston's WFXT-TV, Channel 25.

The Kennedy measure prevents the Federal Communications Commission from waiving rules barring anyone from owning a newspaper and a television station in the same market.

Sen. Daniel Patrick Moynihan (D-N.Y.), who called the hearing, said it is unlikely that Congress will reverse the action.

At the hearing, Koch accused Kennedy of using "a smokescreen of his concern about diversity of opinion" to "launch a noxious assault on the First Amendment." Koch said it was "surprising" that "a staunch advocate of liberalism would subvert liberal principles in the name of hidden self-interest."

In an interview, Koch said Kennedy had engaged in "a vindictive act" that "singled out one person" and "violated any standard of ethical reasonableness."

Rep. Guy V. Molinari (R-N.Y.), said "this has clearly been a personal vendetta on the part of Sen. Kennedy. If every member of Congress were able to shut down a newspaper that was hostile to him or her, there would be no newspapers left in the country."

Kennedy said in a statement that he has "no vendetta" against Murdoch but is trying to uphold laws against media concentration that he considers "a cornerstone of the First Amendment."

Despite the "self-serving hue and cry," Kennedy said, "Rupert Murdoch was doing something very similar at the FCC" in trying to obtain extension of a waiver exempting him from the cross-ownership rules.

The bad blood dates to the 1980 presidential campaign, when Murdoch's Post sent reporters to Europe to find women who claimed to have had liaisons with Kennedy and when it published a series on the 1969 Chappaquiddick accident, in which Mary Jo Kopechne, a passenger in Kennedy's car, died.

The paper ran such headlines as "Ted Cheered Near Grave of Mary Jo" and "Desperate Ted Storms New York."

The Post endorsed then-President Jimmy Carter in the New York primary.

The newspaper's antagonism toward Kennedy has been matched by its fervent support for Koch, whom it all but drafted to run for governor in 1982. Wilbert A. Tatum, chairman of the Amsterdam News, a black weekly newspaper, said today that the Post "belongs to Mr. Koch."

The mayor replied that he was trying to save "a dissenting voice" among New York's newspapers, as well as more than 1,000 jobs. "Shall I only jump to the defense of people I disagree with?" he asked.

Tatum said he wants to buy the Post, which is losing more than $10 million a year but Murdoch has refused to provide enough financial information for him to make a bid. A Murdoch spokesman said Tatum received the same information provided to 11 other potential buyers.

Harry Leykis, representing The Newspaper Guild, said he was "horrified" by Kennedy's move because he always believed "that the Kennedys stood for people like me, working people with open collars and inky hands and families to feed."

Staff researcher Marianne Yen contributed to this report.