The Pentagon on Wednesday opened a second round of bidding for a $35 billion Air Force tanker contract, following the first error-plagued attempt that led to Los Angeles-based Northrop Grumman Corp. and its partner beating out expected winner Boeing Co.

A revised request for proposals has been issued for the new aerial refueling tanker to replace Air Force’s decades-old fleet. Both companies are expected to bid again, and the decision is expected to be announced by the end of the year.

The new round will be limited to eight issues where government auditors found problems with the initial process, according to the Pentagon, with a key focus on certain guidelines for the plane’s design. In the first round, Northrop’s version of the plane was larger than Boeing’s, and the GAO concluded the Air Force unfairly gave Northrop extra credit even though the initial request for proposals included no size requirements for the aircraft.

The Pentagon has scheduled a noon Pacific Time news conference to discuss the revised selection process.

Northrop and Airbus parent European Aeronautic Defense and Space Co. won the original contract, but Boeing protested, saying the Air Force did not conduct the process fairly. A Government Accountability Office review agreed. Defense Secretary Robert Gates said he would reopen bidding, which will be reviewed by a special committee.