Boeing Co said Friday it is studying new draft bidding rules to decide which plane or planes to pit against the rival team of Northrop Grumman Corp and EADS's EADS.PA Airbus in a renewed $35 billion contest to supply refueling aircraft to the U.S. Air Force.

Boeing said it has not yet decided whether to stick with its modified 767 tanker, which lost a previous, canceled competition, or go to a larger 777-based tanker.

The Pentagon spelled out Thursday how the winner of the competition would be picked.

Our next step is to conduct a detailed review of the document, a Boeing statement said. We want to understand how requirements will be defined and prioritized and how the proposals will be evaluated.

That information will help us decide which plane to offer or whether to offer both planes. We appreciate that there will be frequent, open discussion with the U.S. Air Force as we go forward.

Northrop-EADS is proposing a tanker based on the Airbus A-330.

The companies have 60 days to comment on the Air Force's request for proposal, published Friday, before final bidding specifications are released.

(Reporting by Jim Wolf, editing by Gerald E. McCormick)