A move nearly 10 years in the making starts Monday as the Social Security Administration begins relocating 1,600 employees from a massive facility near Lexington Market to a new, trimmer facility uptown.

They leave behind two blocks of empty buildings from 1980, the outdated remnants of a federal plan to inject economic activity into Baltimore's west side — an area still struggling to capture the renaissance occurring in other parts of the city.

The complex's workers, whose numbers have dropped from almost 3,500 in 2001, once generated 20 percent of sales at the nearby Italian deli Trinacria, said Vince Fava, owner of the Paca Street fixture that sells sandwiches, homemade pasta and other gourmet products.

"I remember when it first opened. … At 12 o'clock, you should see the massive amount of people that would come out of there. … It's no more. It's a little trickle now," he said. "It hurt because they're right across the street. I really notice a big difference."

The agency's departure creates a vacuum in an area where stalled developments and ongoing concerns about safety threaten to undermine renewal brought by the expansion of the University of Maryland, new apartments and a nascent arts district anchored by the Hippodrome and Everyman theaters.

The soon-to-be-empty buildings lie a few blocks north of the so-called Superblock, a proposed $152 million mixed-use development, and a few blocks south of the $1.5 billion State Center redevelopment, a 28-acre project meant to host thousands of state workers as well as shops and residences. Both projects remain stuck in litigation.

While the relocation of the Social Security Administration's remaining workers to a new building near the Reisterstown Road Plaza Metro Station isn't a net loss for the city, "it's a big blow to the west side," architect Klaus Philipsen said.

City officials acknowledge that the sheer size of the federally owned Social Security complex will make finding a new occupant difficult.

"We all knew it was going to [open] a great opportunity, but also be challenging at the same time," said Colin Tarbert, the city's deputy director of economic and neighborhood development. "From the city's perspective, we want to make sure the building is secured and it doesn't become a negative in the area because we're working hard to build up the West Side."

Meanwhile, area merchants are watching closely.

"I'm not really sure what they're going to do," said William Gold, the owner-operator of Lexington Liquor Shop, adding that the relocation of the Social Security Administration, the city's 13th largest employer, will hurt his business in Lexington Market. "It's tough for all the merchants in here now. With customers leaving, there's no new customers coming in."

Some in the area believe the University of Maryland, Baltimore has already purchased the Social Security Administration's Metro West complex, but that's not true. There are no firm plans yet for the North Greene Street behemoth, two buildings connected by a sky bridge, and a 14-story tower plus more than 500 parking spaces.

Philipsen, who sits on the Baltimore Development Corp.'s west side committee and whose firm, ArchPlan Inc., is located in the area, believes there has been a lack of planning for the 11-acre parcel, which spans the Mulberry Street side of the Route 40 "highway to nowhere."

"I see a big hulk of buildings is vacant and I'm scratching my head," he said of the Metro West complex, where Social Security employees handled the agency's national 800-number hotline and responded to website inquiries. "How is it possible that [the U.S. General Services Administration] will move to a new location without having any clue what to do with the old facility?"

In August, the GSA, the federal agency that owns the site, hosted an information session to solicit ideas for the property from developers and other entities. At the meeting, which drew about 50 people — more than 20 of them from the GSA itself — GSA officials said they hoped to transfer the acreage in exchange for services, such as renovation at one of the agency's other buildings.

That idea won't work for the University of Maryland, Baltimore, which borders the complex along Saratoga Street and has long been the presumed heir apparent, said university spokesman Alex Likowski.

The school's 2010 facilities master plan identifies the Metro West facility, which completed a $41 million renovation in 2003, as a potential acquisition. But the university cannot ask for state funds to renovate nonuniversity federal structures, Likowski said. "That's something that might work for another federal agency, but it's not a model that we think could work for the university."

The university has other concerns, including the required renovation, he said. "We don't need that much space right now. Perhaps in the future, but we have higher priorities at this time in our research and teaching facilities."

Still, conversations between the GSA and the university are "ongoing," he said.

GSA spokeswoman Gina Blyther Gilliam said the site is suitable for offices or mixed use and the agency received enough responses by its Sept. 23 deadline that it continues to consider an exchange. The GSA expects to announce a decision by the end of the winter, she said.