A development team headed by Western Development Corp., the developer of the controversial Washington Harbour project on the Georgetown waterfront, yesterday narrowly won the coveted right to build a mammoth, $460 million office, hotel and commercial complex on the Portal site at the foot of the 14th Street bridge.

The District's Redevelopment Land Agency voted 3 to 2 in favor of the Western proposal, which the company's officials said by 1993 will transform Southwest Washington's last major redevelopment parcel, now a scruffy 10-acre eyesore, into a glitzy collection of four office buildings, shops, a 600-room Radisson Hotel, and pools of water on a plaza over existing Conrail tracks.

The Rev. Ernest R. Gibson, an RLA board member who skipped last week's meeting to attend a church convention, cast the deciding vote for the Western group, saying that its architectural design, with curving structures, turrets and arches, and 49 percent minority ownership were preferable to that of a second group.

His vote broke a deadlock among the panel's other four members who last week had split evenly on a trio of votes between Western and a development team headed by Washington developer Conrad Cafritz; Boston builder Mortimer B. Zuckerman, who recently bought U.S. News & World Report, and Roger R. Blunt Sr., head of one of the nation's largest black-owned construction firms and the next president of the Metropolitan Washington Board of Trade.

"Western's design [by architect Arthur Cotton Moore] provides impressive substance . . . to those who come across the [14th Street] bridge," Gibson said, adding that Western's "broad minority participation" also swayed his vote.

RLA board Chairman James E. Clay, who also voted for Western, said the complex, because of its architecture, would provide "some representation to the public as they enter the city that there is a statement worthy of the site," compared with the $250 million Cafritz plan that called for construction of nine traditional-looking buildings much like the federal buildings already on the Mall.

"Clearly, a project that's projected to cost more than $400 million," Clay said, "will provide more jobs, more revenue to the city than one that costs $250 million."

The victory for Western is the latest in a string of major projects that city and federal officials have given the Georgetown-based developer the right to build. The firm is nearing completion of the $200 million Washington Harbour condominium and commercial project along the Potomac River that some Georgetown activists fought for years. Western also built one section of the chic Georgetown Park shopping mall and has been awarded development rights for the Market Square site between Seventh and Ninth streets NW along Pennsylvania Avenue.

The Portal site, bounded by 12th, 14th and D streets and Maine Avenue SW, is now filled with weeds, parking lots, Conrail tracks and a General Services Administration facility that literally shakes coal to break it apart.

Nonetheless, Herbert S. Miller, Western's board chairman, enthusiastically described the parcel as "one of the greatest sites in the United States." He said the complex will add "a center of vitality" to the Southwest waterfront.

Miller said his development team has a "letter agreement" with Conrail officials, but no contract, to build a deck over the rail line's tracks and is negotiating with GSA about "building around or over" the coal-shaking facility. A Conrail spokesman said the railroad is willing to discuss the construction project further.

Under terms of the redevelopment agency's decision, Western has 120 days to negotiate with the city to purchase the Portal site, which the RLA has appraised as worth $51.6 million.

In the meantime, Western has to pay the agency a nonrefundable $50,000 fee each month as evidence of its intention to complete the deal.

Three years ago, the agency tried to start redevelopment of the site, but the RLA eventually broke off land price negotiations with the team it selected then, Banneker Associates, which included shopping center magnate Theodore N. Lerner and developer Melvin Lenkin. This time, the agency has already decided to try to work a deal with the Cafritz group if negotiations should fall through with Western's group.

Miller said construction on the first phase of the project, including 400 of the hotel rooms, will be started late next year and be completed within two years.

Western controls a 49 percent interest in the project. Its team, formally called Portals Development Associates, also includes a minority-owned contractor, Eastcoast Development Corp., with 8 percent interest and eight Washington residents who have 2 to 8 percent interests in the venture.

They are restaurateur Manuel V. Fernandez; lawyers Carolyn Jordan and David Wilmot; arts advocate Marie Barksdale; Carlton Jones, a real estate agent, and John Clyburn, Roy Littlejohn, and Robert Mendelsohn, all consultants.

As Gibson announced his intention to vote for Western, Cafritz, sitting in the audience, bowed his head. Later, asked for his thoughts on the decision, Cafritz hurried away, saying, "I have lots of thoughts but no comments."

Board member Kwasi Holman, head of the city's Office of Business and Economic Development, joined Clay, former head of the city's housing department and now a city economic and development official, and Gibson in voting for Western. Stephen Klein, an energy policy adviser for the Agency for International Development, and Judith E. Jenkins, a lawyer, voted for the Cafritz plan, as they did last week.