NEW YORK (AP) _ A union official whose cooperation was considered crucial to saving the New York Post boycotted labor-management negotiations Wednesday, with a deadline for closing the paper two days away.

Jerry Cronin, president of the 350-member drivers' union, did not join the negotiations. Both sides had said agreement was impossible without the cooperation of his union.

Late in the day, the Post announced that arbitrator Thomas G. Christensen, a labor law professor at New York University, had denied a petition by the drivers' union to stop the paper from closing Feb. 19.

The union argued that the Post was required by contract to give 30 days' notice of any change in work rules, Rubenstein said. Christensen decided that the rule did not apply if the paper was closing.

''The newspaper hopes that the drivers will now work with them in reaching an agreement,'' said Howard Rubenstein, a spokesman for the Post.

Cronin could not be reached for comment.

Earlier, labor lawyer Theodore W. Kheel, who is advising the newspaper's union, had said ''there's no chance of a settlement before Friday.''

The talks, billed as a round-the-clock session, adjourned Wednesday night after the unions offered a plan they said would save the paper's new owner $24 million while still providing a raise for 1,200 employees.

''We tried hard today and we think we made some headway with a proposal that made sense,'' said George McDonald, president of the Allied Printing Trades Council, an umbrella group for eight Post unions.

Post publisher Patrick Purcell had no comment as he left the session. More talks were scheduled for Thursday morning.

Post owner Rupert Murdoch has demanded $24 million in union givebacks as a condition of a $37 million sale of the paper to real-estate developer Peter Kalikow. Murdoch has threatened to close the paper Friday if the union does not agree.

One union leader, Lenny Higgins of the pressmen's union, said one goal was to extend the deadline. ''If he (Murdoch) stays with the Friday deadline, I don't know what'll happen,'' he said.

Under the terms of his contract with Kalikow, Murdoch has until Monday to negotiate the union concessions.

Murdoch opted to sell the Post after Congress passed legislation preventing cross-ownership of a newspaper and a television station in the same city. Murdoch also owns WNYW-TV in New York. He faces a similar cross-ownership situation in Boston.

Murdoch claims he has lost nearly $150 million since purchasing the Post 11 years ago.