The race is officially on for one of the hottest development sites in Greater Boston.

The federal government on Wednesday issued a formal request for proposals for the 14-acre campus of the Volpe Transportation Center in Kendall Square, offering up a rare swath of open land in one of the tightest real estate markets on the East Coast. Developers will have 90 days to respond with their plans, and the General Services Administration hopes to award the site to one of them by year’s end.

A slew of major Boston-area builders have expressed interest in the site, according to Cambridge officials, among them Skanska USA, Boston Properties, Alexandria Real Estate Equities, and the real estate arm of the Massachusetts Institute of Technology.

The GSA released the RFP only to bidders who qualified in an earlier round of the competition, which included proven ability to finance a $500 million project. The agency has declined to identify those firms, citing federal procurement laws. It has also refused to publicly release details of the RFP, so it is unclear what priorities the agency will consider.

One requirement the GSA did disclose, however, is that the winning bidder build a “state-of-the-art’’ facility for the Volpe Center itself before taking possession of the rest of the property. That means any large mixed-use development there is likely to be years away.

It’s not clear what form that development might take, or how big it could be. Late last year, Cambridge officials halted a plan to rezone the Volpe site for the new project until a developer was selected. The city was considering allowing a building as high as 500 feet, which would be the tallest in Cambridge, along with adopting steep requirements for affordable housing and open space.

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.