SAN JOSE — A big mixed-use development on the eastern side of downtown San Jose is headed for a possible makeover because the government agency slated to occupy the site might wind up at another location in the city.

The Santa Clara County Housing Authority has been working toward a dramatic redevelopment of a vacant lot at 675 E. Santa Clara Street whereby the agency would be the anchor office tenant — but now it’s possible the government entity will establish its main offices elsewhere.

Regardless of the Housing Authority’s decision for its primary location of the future, a redevelopment of what is now a blighted and vacant parcel is deemed to be a major upgrade for the property.

“We are hoping our development will enliven the neighborhood,” said Katherine Harasz, executive director of the Santa Clara County Housing Authority. “It’s an area that’s been a grassy field for a little too long a time.”

Residences, offices, retail, a public plaza, and a county customer service operation would be the primary uses for the mixed-use development at 675 E. Santa Clara St., San Jose city planning documents show.

“Our neighbors are ready to see some activity at this site and we are ready to provide it,” Harasz said.

A very preliminary proposal that’s been filed with the city planning department envisions 360 new residential units and 100,000 square feet of office space, along with ground-floor retail, a large public plaza, and a county service center, according to the city planning documents.

The Housing Authority was expected to be the anchor of the office component in the proposed development, which would front on East Santa Clara Street between North 14th Street and North 15th Street.

At present, the housing agency occupies cramped quarters at 505 W. Julian St. in downtown San Jose near the sites of two major anticipated developments, Google’s Downtown West transit village and the Platform 16 tech campus being built by Boston Properties.

The county agency has now begun to scout for a location on North First Street in San Jose. Under one scenario under active review, the housing organization would purchase the property.

Harasz didn’t want to immediately disclose the North First Street site because the county Housing Authority is conducting due diligence.

However, the sites of a recently closed McDonald’s restaurant at 2040 N. First St.and an adjacent E-Z 8 Motel at 2050 N. First St. are believed to be up for sale.

If the Housing Authority proceeds with its North First Street option, one scenario for 675 E. Santa Clara would be a development with 510 residences, an increase of 150 dwellings from the current preliminary plans of 360 domiciles.

“We are looking for some flexibility in case we go through with the acquisition of an existing building,” Harasz said. She added, “It could be more cost-effective” to purchase a building and re-purpose it for the Housing Authority.

The prospect of new scenarios for the East Santa Clara Street property jolted one development expert, Bob Staedler, principal executive with Silicon Valley Synergy, a land-use consultancy.

“It’s a little disappointing that the Housing Authority hasn’t gotten this figured out already,” Staedler said.

Redevelopment of the East Santa Clare property is crucial, Staedler opined.

“It’s a blighted area with vacant parcels,” Staedler said. “Something needs to happen on this site.”