WASHINGTON (AP) _ Boeing says the Air Force tilted the playing field in a tanker contract competition toward Northrop Grumman and the French owner of Airbus to keep the two in the game.

Boeing's formal protest of the contract was made public Tuesday.

The plane maker said the Air Force "repeatedly made fundamental but often unstated changes to the bid requirements and evaluation process" to keep the Northrop Grumman-Airbus proposal alive.

The release of the executive summary of the protest is Boeing's latest salvo in its attempt to overturn the Air Force decision. Doing so won't be easy -- a fact a Boeing executive acknowledged Tuesday while predicting the company would prevail.

Kansas officials say the Wichita area would gain up to 500 jobs and 3,800 statewide if the 35 billion-dollar contract would go to Boeing.

(Copyright 2008 by The Associated Press. All Rights Reserved.)