By: George Garneau THE FEDERAL Communications Commission, within days after Rupert Murdoch threatened to close the New York Post, granted an unprecedented waiver of FCC cross-ownership regulations. The FCC voted 2-1 to allow Murdoch's News Corp. to own both the Post and WYNY-TV. The waiver clears a major obstacle from Murdoch's path to reacquire the money-losing Post, which he was forced to sell in 1988. But he still must win final approval from a bankruptcy court, and that will require heavy concessions from the paper's unions, whose members have lived on the brink of joblessness for months. Murdoch emerged last spring as a buyer of last resort as the paper was being passed from hand to hand by a series of unconventional businessmen whose stewardship nearly killed it. He is seeking to buy back the Post from Peter Kalikow, who bought it from Murdoch in 1988 and whose real estate problems drove him to bankruptcy court last year. Murdoch has operated the Post since March under a temporary waiver, pending a permanent waiver and bankruptcy court approval. Angered at two months of FCC inaction, Murdoch threatened to close the paper, which he says is losing $300,000 a week, unless the FCC moved. The FCC concluded that the waiver would not hurt media competition, but would give the bankruptcy court a choice from "a full complement of purchasers." Acting FCC Chairman James H. Quello, a Democrat, said he voted for the waiver to save the jobs of 700 or so Post employees. Opposing the waiver, FCC commissioner Andrew C. Barrett, a Republican, argued that it could open the door to media mergers in other cities. In other developments, the Post's unions begged the FCC to grant Murdoch the waiver because they were "convinced" it would fold otherwise. Also, another would-be buyer, Connecticut businessman Mahmoud Wahba, withdrew his proposed offer.