The Bush administration has decided to abandon the effort by Michael K. Powell, the outgoing chairman of the Federal Communications Commission, to relax the regulations that have prevented the nation's largest media companies from growing bigger and entering new markets, government officials and industry lawyers briefed about the decision said today.

In a final slap at Mr. Powell, the Justice Department will not ask the United States Supreme Court to consider a decision last year by a federal appeals court in Philadelphia that sharply criticized the attempt to deregulate the rules and ordered the commission to reconsider its action.

Big media companies have been urging the administration to get involved in the case. But its decision not to recommend that the Supreme Court take the case sharply reduces the odds that the justices would intervene. The court had set next Monday as a deadline for the parties to file their initial papers in the appeal.

Officials said one reason the administration decided not to seek Supreme Court review is that some lawyers were concerned that the case could prompt the justices to review related First Amendment issues in a way that could undermine efforts by the commission to enforce indecency rules against television and radio broadcasters. Over the last year, the agency has issued a record number and size of fines, and has been pressed by some conservative and other advocacy groups to be more aggressive.

If, as now expected, the appeals court decision withstands legal challenge by some media companies, it would prevent the biggest media conglomerates from expanding.