Neustar — the Sterling-based company that for 17 years has held an exclusive government contract to provide the technology that enables U.S. cellphone users to keep their numbers when they switch carriers — is in danger of losing the work to a rival bidder.

Neustar’s contract to provide “number portability,” which must be approved by the Federal Communications Commission, is slated to expire next June. Neustar and rival bidder Telcordia, a unit of the Swedish telecom giant Ericsson, have been fighting over the contract for months.

On Monday, the FCC said a panel that advises the agency about number-portability issues recommended that the FCC award the contract to Telcordia.

Members of the North American Numbering Council “unanimously reached this recommendation, with one abstention vote, in a closed meeting on March 26, 2014,” an FCC filing said. The contract is a critical part of Neustar’s business, and losing it would severely cut into its revenue. In 2013, the contract was valued at $450 million, nearly half of the company’s 2013 revenue of $902 million. Neustar, which has about 1,600 employees globally, including nearly 800 in the Washington area, was founded in 1996, primarily to provide number-portability services. Neustar has had the contract renewed, uncontested, until now.

Telcordia provides number-portability services in India.

Word of the recommendation was leaked Friday, when an e-mail alluding to the decision was inadvertently posted on an FCC Web site, a disclosure Neustar called troubling.

An FCC spokesman declined to comment on the release of the e-mail, saying the agency is seeking public comment on the recommendation.

Joel Fisher, a spokesman for Telcordia, said the company is pleased that the council has recommended Telcordia to serve as the next vendor for number portability.

“That such a diverse group of industry and consumer representatives is urging the FCC to select Telcordia shows their confidence in our ability to be an exceptional partner,” Fisher said in a statement.

Neustar  shares fell Monday 8.4 percent, to $24.43, after word of the group’s recommendation became public.

“The [council’s] recommendation is by no means the end of the process,” Neustar said in a statement Monday morning. “Neustar intends to continue to compete vigorously in the [number portability] vendor selection process, and to advocate strongly that we are the logical choice to remain as administrator.”