Real estate development in the District can be a rough-and-tumble sport. But few people can recall the type of ball game -- akin to tackle football without a helmet -- being played in recent weeks by two federal agencies over a plan to renovate the city's old main Post Office building next to Union Station.

A representative of a team of developers and U.S. Postal Service officials, proposing the rehabilitation of the mostly empty structure at Massachusetts Avenue and North Capitol Street, could not contain himself when asked about the National Capital Planning Commission, the agency considering the proposal. "There's a level of deviousness here that is extremely upsetting," he said. "It's just infuriating."

"They've lied to us; they've misrepresented things," responded a representative from the opposing camp, made up of the planning commission staff and community activists. "It's extraordinary."

The bitterness has been mounting for 11 months between the Postal Service and the planning commission, two usually noncontroversial federal agencies that are locked in a battle royal over the District's most expensive private rehabilitation project. A showdown is set for Nov. 5, when the 12-member planning commission board is expected to vote.

The stakes are big time. Since last year, when 4,000 mail-sorting employes moved from the huge 73-year-old structure to a new facility in Northeast Washington, the Postal Service has planned a lush $140 million renovation, including an office complex and a new Smithsonian Institution stamp museum.

Last year, the Postal Service chose a group of developers to renovate the building. The project is crucial to the surrounding neighborhood, which has been waiting for a predicted development boom, and to the adjacent Union Station, which is undergoing a $150 million rehabilitation into a retail complex that needs the 4,400 office workers -- and potential shoppers -- the Post Office building would provide.

The snag lies with the Postal Service's claim that to finance the museum and renovation, it needs to build an office complex in the structure's courtyard that would extend above the current roof line by 1 1/2 stories.

That plan angers historic preservation activists, who believe the addition would violate a 1910 federal law limiting the height of buildings near Union Station. The staff of the planning commission, which oversees construction on federal property in the District, and the agency's board chairman, Glen T. Urquhart, agree.

Because the two federal agencies disagree about the law's applicability, they have asked the Justice Department to resolve the matter.

For a year, the planning commission has held the fate of the project, delaying it month after month to get more information from the developers -- a joint venture of two New York real estate firms, Julien J. Studley Inc. and Arthur G. Cohen Properties Inc.

Frustration has mounted among the developers and postal officials, who have taken a step that is virtually unprecedented in the recent history of the low-key planning commission: going over the commission staff's head and lobbying the board members and their bosses.

Urquhart expressed frustration that applicants before the commission would use that tactic.

"In my experience, it certainly is unusual for a government project to be lobbying another government agency like ourselves," Urquhart said. Another project opponent is more blunt: "There's a huge amount of pressure involved."

Developer representatives believe the commission staff is biased against the proposal and has been preventing the board from receiving key information.

Gerald Carmen -- administrator of the General Services Administration in President Reagan's first term and now a publicist working for the Post Office developers -- bridled at the suggestion that his efforts on behalf of the project are out of bounds. "They're not used to the democratic process," Carmen said of the commission staff. "It's simply a group of bureaucrats that are used to getting their way."

Carmen and Postal Service officials have spoken to most planning commission board members and their higher-ups, sources said. Among those contacted were officials of the GSA, which holds a planning commission seat; D.C. officials, who have four seats; W. Don MacGillivray, a Reagan appointee from California; John Parsons, a National Park Service representative who occupies the Interior Department's planning commission board seat; and top Interior officials.

Parsons did not return telephone inquiries, and an Interior spokesman said it has not decided how to vote. But sources said that Parsons has expressed doubts about the project, and that Carmen's contact with Interior has tilted it toward a "yes" vote.

Members of the development team also raise a number of angry accusations, such as that the planning commission staff doctored area maps bolstering its position. Commission officials scoff at the suggestion, saying their maps were drawn from historical documents.

At the heart of the controversy is the massive granite structure, designed in the Beaux Arts style by Daniel Burnham, Union Station's architect. Its high, vaulted lobby, with bronze paneling and marble floors, needs a complete makeover, officials said.

The postal history and stamp museum that the Postal Service wants to build in the basement has been on that agency's wish list for years. It would replace the cramped one in the Museum of American History, and would house the Smithsonian's stamp collection, which is the world's finest.

But Postal Service officials have said, essentially: No addition, no museum.

The plan is for the Postal Service to lease the building to the developer, which would pay for renovation and then lease space in the existing building to government agencies at fairly low rents. The developer would lease space in the addition to private tenants for higher rent.

The commission's Urquhart said the tradeoff he sees -- compromising historic preservation standards to build a museum -- is unsavory.

"We think the U.S. government should be providing leadership in historic preservation," he said. "Otherwise, how morally can I stand before the development community . . . and say, 'You can't add two floors to this building'?"

Historic preservationists back him. Michael Quin, executive director of the D.C. Preservation League, said in a statement that "the city Post Office should be accorded greater respect."

But after the developers lopped off a top floor from their plans, Carol Thompson, D.C.'s deputy mayor for economic development, who was acting in her role as the city's historic preservation officer, approved the addition.

Stephen Porter, the developers' attorney, said that the idea that the addition would be a precedent for defacing monuments is "absurd." "We can't convince {commission staff} that we're being sensitive to historic preservation concerns," Porter said. "We're not antipreservation . . . . The people are the losers if a reflexive antidevelopment stance is taken."

Legally, the main issue in dispute is whether the 1910 federal law applies. The law limits the height of buildings throughout the city, and specifically limits to 80 feet any structures abutting the semicircular Union Station Plaza in front of the station. The top of the proposed addition would rise to 102 feet.

The Justice Department is examining hundreds of pages of documents and 75-year-old maps submitted by both sides. The developers are saying that the law does not apply to federal buildings, and that the building doesn't "abut" the plaza, since it is more than 200 feet from it. They add that the addition is hardly visible from the plaza.

But Urquhart disagrees, and fears the project would create a dangerous precedent. "You don't build condos on the White House lawn just so you can knock $10 million off the deficit," he said.