Rupert Murdoch yesterday threatened to "padlock" the New York Post at 2 p.m. on Feb. 19 unless the Post's 1,200 employees agree to an immediate 12 percent pay cut, a three-year pay freeze and loss of almost 80 jobs, according to newspaper union representatives.

Murdoch told union leaders during a brief session yesterday morning that unless they agreed to the package -- which would save the paper $24 million in three years -- he would not be able to comply with his contract to sell the paper to Manhattan real estate developer Peter Kalikow for $37 million.

"We've been used," said Barry F. Lipton, president of the Newspaper Guild, the largest union at the Post. "We were doing our damndest to try to help him get an extension {on federal rules that require him to sell the Post} and he's trying to jam us.

"It's obvious that if the paper does close, he wants to be able to blame the unions," Lipton said.

"If Feb. 19 comes and this paper closes down, it will be Rupert Murdoch who closes it down, not the unions," said George McDonald, president of the Allied Printing Trades Council and spokesman for eight of the unions at the paper.

Besides the cuts, union representatives are upset that Kalikow was not asked to sign an agreement to keep the paper open for three years, as originally expected. Murdoch told the union representatives that it would cost Kalikow another $40 million in liabilities to close the paper, and that he would not.

Jerry Cronin, president of the drivers and mailhandlers union, said that he walked out of the session with Murdoch and his representatives because Kalikow was not present to lay out his plans for the paper.

"Why are they shielding Mr. Kalikow? I know why. He won't answer the magic question. The magic question is how long will he keep the joint open," Cronin said.

Kalikow said in a statement after the sale was announced Sunday that he would keep the paper alive. "I will not sit on the sidelines and watch another New York institution become a memory," he said.

The Post, a racy tabloid valued as much for its headlines as its news content, has been losing more than $10 million a year, with losses estimated at $17 million last year.

Some of those familiar with Murdoch's management of the paper since he bought it in 1976 say he has lost between $100 million and $200 million. Although Murdoch has said that the property is worth $35 million, other experts in New York real estate said that estimate was "very high," as one put it.

Efforts by Murdoch to sell the Post have intensified since December, when Democratic senators attached an amendment to the omnibus spending act that barred the Federal Communications Commission from giving Murdoch any extra time to sell either the Post or a New York television station.

The FCC had already given Murdoch almost two years to sell one of his New York properties under its "cross ownership" rule, and Democratic senators Edward M. Kennedy (Mass.) and Ernest Hollings (S.C.) said they saw signs that the commission planned to give Murdoch more time or even abolish the rule.

Although Murdoch has announced the contract with Kalikow, his lawyers told the FCC that they are continuing to pursue an appeal to overturn the Kennedy-Hollings amendment as unconstitutional. The court scheduled a hearing on the appeal for Thursday.

Labor lawyer Theodore Kheel told reporters yesterday in New York that he has asked to see the agreement between Murdoch and Kalikow so that he can come up with a proposal for the employees of the Post to buy the paper.

Another potential buyer, Leonard Stern, who owns Hartz Mountain pet products and The Village Voice, said that it would be difficult for him "now to construct a scenario where we would become an active player.

"Time is against us now. I think you're going to see an enormously hostile situation with labor over there, and the day-by-day deterioration of the advertising support makes it all the more difficult," Stern said. "I really wanted a shot to keep it alive, but I guess I'm not going to get it."

Another potential buyer of the Post, Wilbert Tatum, majority owner of the New York Amsterdam News, said yesterday that he believes the sale of the Post is "highly suspicious and leaves considerable doubt that the Post has been or will be sold in a manner sufficient to satisfy the cross ownership rule.

"It's a deal that's not a deal," Tatum said. "It's called playing for time and seeing where the courts go."

Tatum, a longtime critic of Murdoch, said in papers filed with the U.S. appeals panel that he had to threaten to sue Murdoch to begin the process of trying to make a bid for the paper.