Chief Executive Eileen Drake and Warren Lichtenstein, the executive chairman, each proposed eight director candidates to sit on the board.

Investors will vote on director candidates on June 30.

Glass Lewis acknowledged Lichtenstein's long service, but said investors should back Drake's slate because the company has performed well and generated value for investors during her tenure. The firm praised Drake for putting together an "experienced and well-rounded slate of candidates in short order."

Institutional Shareholder Services on Friday also backed Drake's slate.

The standoff between Drake and Lichtenstein, whose Steel Partners and affiliates own more than 5% of the company, escalated since the collapse of a planned sale of Aerojet to Lockheed Martin Corp, the company's biggest customer.

"We are very gratified to have received Glass Lewis' full support for our independent slate. We now have the validation of the two leading independent proxy advisory firms," Drake said in a statement.

A representative for Lichtenstein could not be reached for comment.

Lichtenstein argued that operational improvements and changes to capital allocation are needed to help push up the share price and attract new buyers. He wants to bring back Mark Tucker, a former Aerojet chief operating officer, as CEO.

Glass Lewis said Lichtenstein's slate is full of "nominees personally or professionally proximate to Mr. Lichtenstein, including CEO-in-waiting Mark Tucker," which raises concerns that such a board might not "hold Mr. Lichtenstein to account."

(Reporting by Svea Herbst-Bayliss; Editing by Leslie Adler)

By Svea Herbst-Bayliss