A downtown landmark that has languished in total vacancy for more than two years could soon welcome a new tenant if the Planning and Zoning Commission approves a site plan application for a new office center at the property.

The P&Z was scheduled Thursday night to begin its review of a proposal by Greenfield Partners, a Norwalk-based commercial real estate firm, to relocate its corporate headquarters to National Hall, a red-brick Italianate building that stands on the west bank of the Saugatuck River.

Greenfield Partners' site plan calls for converting National Hall into an approximately 18,400-square-foot office center on three floors. The proposal also envisions about 1,100-square-feet of first-floor retail space and an approximately 1,600-square-foot glass-facade addition to National Hall. Accompanying the building work, Greenfield also plans a public lawn and new sidewalk adjacent to National Hall.

"With the combination of office use, small retail use and the two restaurants that are currently being applied for at 6 and 12 Wilton Road, it will start to bring some life back to this side of the river," said Coe Consulting LLC project manager Anil Khachane.

Coe Consulting's president, Mark Coe, also heads Coe Development and Coe Management. The former firm is developing National Hall for Greenfield Partners, while the latter company serves as the National Hall property manager.

Greenfield's proposed redevelopment of several properties it owns in the National Hall complex on the west side of the Saugatuck River arguably represents one of the most ambitious and contentious land-use projects in downtown Westport in the last decade. Alongside its planned office center at National Hall on Post Road West, two site plans have been submitted to the P&Z for new restaurants at 6 and 12 Wilton Road. Greenfield also plans to eventually bring in another restaurant tenant and lease office space at 20 Wilton Road, a vacant building that overlooks the Saugatuck River.

In December 2009, the P&Z approved a text amendment proposed by Greenfield for the Historic Design District, which includes National Hall. That package of zoning changes would have created the regulatory framework for an office center at National Hall. At the time, Greenfield was a prospective buyer looking to acquire National Hall from its then-owner, Antares Investment Partners.

A pair of west side merchants, Age of Reason toy store owner Dina Berger and Mandarin Collection antique shop owner C.C. Wong, subsequently appealed the text amendment approved by the P&Z to the Representative Town Meeting. In January 2010, the RTM upheld the petition, which ruled out Greenfield's office plans for the site.

Two months later, the building's then-occupant, the Inn at National Hall, closed. The boutique hotel had operated at the site since 1993. In April 2010, a Greenfield affiliate acquired the mortgage on the property and later foreclosed on it. Greenfield now owns the landmark.

In October 2011, the P&Z approved a text amendment proposed by Greenfield, which included a set of regulatory revisions for the HDD similar to the text amendment endorsed in December 2009.

The new text amendment removed a ban on office use on the first floor of National Hall and eliminated a cap that limited office use to 10 percent of the total gross floor area of all buildings in the HDD.

No citizen appeals were filed against the October 2011 amendment.

In another move related to the redevelopment of National Hall, the P&Z approved in March a third-level addition to a Greenfield Partners-owned parking deck on Wilton Road, which would be used by employees at the new office center. That expansion will raise the parking structure's capacity from 97 to 133 spaces.

Creating more parking for the National Hall complex appears to have defused much of the opposition to Greenfield's relocation to the downtown landmark. Several neighboring business owners, including Wong, now say they are receptive to a new office center at National Hall.

"The new parking lot addition has addressed a big concern," he said. "We think that these guys have approached this with a reasonable amount of effort and goodwill."

Wong urged P&Z members, however, to consider the prospective redevelopment's impact on traffic at the nearby intersection of Post Road West, Wilton Road and Riverside Avenue.

"This plan makes that issue even more important," he added. "Everybody in the area is aware of the serious congestion problems at that intersection during the peak period. The town should look at that intersection and consider adding some manpower such as a police officer to direct traffic there during rush hour."

Greenfield's proposed redevelopment of the National Hall complex has also garnered the support of several prominent downtown planning figures, including Lou Gagliano, chairman of the town's Downtown 2020 Committee.

"I think it's a very positive move for the west side of the river," Gagliano said. "It will increase the commercial interests of everyone in the downtown area. If you have new restaurants on that side of the river and link them with a new cinema on other side of the river, that's the kind of synergy we'd like to achieve downtown."

If the P&Z approves Greenfield's site plan, Coe said in an email Thursday that "our goal is to have the space ready for our client [by] summer 2013."

Built in 1870, National Hall has housed a variety of occupants during its existence, including a bank and a furniture store.

The P&Z's review of Greenfield Partners' site plan for National Hall is set to continue at a meeting scheduled at 7 p.m. on Thursday in the Town Hall auditorium.

pschott@bcnnew.com; 203-255-4561, ext. 118; twitter.com/paulschott