Amtrak is resuming its search for an overseer to begin redeveloping its vast University City land holdings around 30th Street Station after putting the effort on hold last year amid signs that Philadelphia officials intended to propose nearby sites to Amazon for its planned second headquarters.

The rail operator's renewed call this month for a master developer identifies improving the 1930s station's retail offerings, office space and mechanical systems as the first steps toward completing a decades-long initiative known as the 30th Street Station District Plan, which eventually may include capping nearby rail yards so they can be built over.

In Amtrak's previous "Request for Qualifications" from developers wanting to lead the project last summer, the rail company targeted surrounding parcels, in addition to the station itself, for the plan's first phases.

That solicitation was withdrawn in October after moves by the city to pitch Brandywine Realty Trust's adjacent Schuylkill Yards project to Amazon.com Inc. for its new corporate campus, which the Seattle company has nicknamed HQ2. Philadelphia also pitched Amazon on the uCity Square development to the west of Schuylkill Yards.

With Philadelphia now among 20 localities across North America shortlisted for the project, Amtrak "felt the time was right to go back out to the market," Beth K. Toll, a spokeswoman for the rail company, said Thursday.

"Postponing the RFQ allowed for additional market analysis and research to rescale the scope of the project to align with near-term market demand," she said. "The result is a focus on the station, first and foremost."

The district plan was devised through a two-year, $5.25 million study published in 2016 by a group led by Amtrak, SEPTA, Drexel University, developer Brandywine and the Pennsylvania Department of Transportation.

It envisions the redevelopment over 35 years of what would be a 175-acre site — including capped railyards — between Walnut and Spring Garden Streets, east of the Drexel University campus and Powelton Village.

In its first crack at securing a developer to begin that work, Amtrak included among its first phases the reconfiguration of the public plaza around the rail station for easier pedestrian access and the redevelopment of a now-vacant 32,500-square-foot tract known as Parcel 1 just to the building's west.

In the new, more-station-focused RFQ, Amtrak sets as a priority more and better shopping and restaurant spaces in the building to tap what is thought to be $200 million in unmet spending potential in the area, according to the solicitation document. Amtrak has said it envisions shopping kiosks in the station's main atrium, the replacement of the current South Concourse food court with a food hall, and a bar and lounge in the now little-used North Concourse.

The new solicitation also calls on developers to revamp the building's 220,000 square feet of usable offices now occupied by Amtrak, so the rail company can be consolidated into half of that space and the rest renovated for another commercial use. In addition, the building has about $92 million in immediately necessary infrastructure upgrades, including repairs to its climate-control and mechanical systems, according to the document.

"The development must transform the historic station building into a vibrant destination rather than just a pass-through facility," the company writes in the request. "Development at the station will provide opportunities for commercial amenities and civic assets that welcome and serve travelers, residents, students and visitors."

Also included in the RFQ are second-phase projects, which entail the improvements to the public plaza around the station and the construction of a new transit concourse in a north wing of the station that's now used for parking. Another phase-two project is the planned underground passage linking 30th Street Station with SEPTA's Market-Frankford Line, which is envisioned in the document as a shop-lined promenade.

The request does not entail any work on new development sites surrounding the station, partly to leave Amtrak's options open in case Amazon selects sites in University City for its HQ2 project, Toll said.

In its pitch to Amazon last year, Philadelphia officials highlighted the availability of Amtrak's property as a supplement to the area's other development sites.

"Should Amazon select University City as the location of its second corporate headquarters, there is an additional 58 acres of adjacent Amtrak property north of the station for potential air rights development," Toll said.