BY MIKE ESTERL

The U.S. and Japan reached an “open skies” pact late Friday that will ease restrictions on cross-border flights and possibly open the door to far-reaching alliances among the countries’ major airlines.

But the bilateral accord, following a decade of on-again, off-again talks, is contingent on Japan’s two largest airlines, Japan Airlines Corp. and All Nippon Airways Co., winning antitrust approval to cement joint ventures with large U.S. carriers. Such antitrust approval could take six months or more.

Delta Air Lines Inc. and AMR Corp.’s American Airlines, the two largest U.S. carriers, are aggressively courting JAL, Japan’s financially strapped flagship airline, …