SAIC, the eighth-biggest federal contractor, has lost a protest it filed seeking to overturn the award of its largest contract to Lockheed Martin.

Lockheed on June 15 beat SAIC for the Defense Department deal valued at as much as $4.6 billion to operate a communications network.

The U.S. Government Accountability Office, which arbitrates contract disputes, last week denied SAIC’s protest of the decision, said Ralph White, the GAO’s managing associate general counsel for procurement law.

The Defense Information Systems Agency’s evaluation of Lockheed’s proposal was “reasonable and consistent’’ with the solicitation’s evaluation criteria, White said in an e-mailed statement.

SAIC had accused the agency of “unreasonably’’ evaluating Lockheed’s proposal for technical risk and cost, and of failing to “meaningfully’’ investigate a potential organizational conflict of interest. The GAO denied SAIC’s protest on each count, White said.

SAIC officials declined to comment, company spokeswoman Melissa Koskovichsaid in an e-mail.

Gerry Fasano, president of the Lockheed unit that won the contract, said the Pentagon conducted a “highly competitive and comprehensive bidding process’’ for the project.

“We have remained transition-ready throughout the protest period and look forward to beginning work on this critical mission,’’ Fasano said in an e-mailed statement.

The network contract is for as long as seven years if all options are exercised, and its estimated value for the three-year base period is $1.91 billion, Alana Casanova, a spokeswoman for the Defense Information Systems Agency, said in an e-mail.

SAIC, based in McLean, has received at least $4 billion to operate the network since 2002, according to government data. The network is known as the Global Information Grid.

— Bloomberg Government