MINNEAPOLIS — The federal body that oversees airline labor relations is withdrawing a proposal that critics said would have made it harder to keep unions in place when airlines such as Delta and Northwest combine.

In a notice issued Thursday, the National Mediation Board wrote that it had been aiming to clarify existing policy about how union representation is transferred in a merger where one carrier has unions and the other does not.

Pilots are the only large union at Delta Air Lines Inc., while all front-line workers at Northwest Airlines Corp. are unionized. Delta is acquiring Northwest in a stock-swap deal they hope will close around the end of this year.

"Due to the concerns and confusion expressed by the commenting parties, the board has decided that it will not implement the manual revision proposals at the current time," mediation board General Counsel Mary L. Johnson wrote in the notice.

The three-member board made the proposal on July 15, two weeks after Read Van de Water became chairman. She had been Northwest Airlines' director of government affairs — its chief lobbyist — until 1997.

The lone Democratic appointee on the board, Harry R. Hoglander, had publicly opposed one part of the proposal, writing on Aug. 15 that it had prompted the perception that the National Mediation Board is "biased in favor of carriers in general, and Delta Airlines in particular."

Hoglander was referring to a provision that the unions said would have made it tougher to continue certification after an airline merger. In cases where a union represents workers at one merger partner but not the other, the NMB proposed to "exercise its discretion and extend the certification only where there is more than a substantial majority, as determined by the board."

That struck the unions as far too vague, and they wondered why the board was in such a hurry to adopt it.

Edward Wytkind, president of the Transportation Trades Department at the AFL-CIO, said it looked like the board was working in advance of the election to make it harder to keep unions at merged airlines. The board's three members are appointed by the President, though only two can be from the same party.

"This was clearly a sop to the employer community with the hope they could secure rules" more favorable to employers, he said.