The discussion started out genteelly enough. Officials of exclusive National Cathedral School visited their Cleveland Park neighbors and, in the privacy of living rooms, chatted about plans to build a new school gym. But soon, it turned into a high-stakes brawl, pitting well-heeled homeowners against august Washington National Cathedral.

Crowded zoning board hearings with Adolfo-clad matrons in attendance. Heated community meetings, including one where a neighbor -- after being told he should feel free to leave the neighborhood -- accused the other side of the "ethnic cleansing of Cleveland Park." Homeowners banding together into an association with the money to hire two land-use lawyers plus an engineering consultant to fight the project. Parents fighting the school their own daughters attend.

The battle over the NCS gym is expected to be settled today by the District's Board of Zoning Adjustment. In the meantime, as one longtime neighbor said, the debate has taken on a "mini-Disney quality."

"This is the rich and powerful," said the neighbor, who asked for anonymity, "and these people are not going to take this lying down."

The proposed structure is not just any old gym. The school, which sits on the 57-acre campus of Washington National Cathedral and is overseen by the Protestant Episcopal Cathedral Foundation, wants to build a $20 million project that would include an 83,160-square-foot athletic facility -- with all but 4,360 square feet below ground -- and an adjoining 50-space underground parking garage. It would occupy 16,000 square feet.

If built, both proponents and opponents agree, the facility would be four times larger than the biggest athletic facility at a local girls' independent school.

Neighbors say a year-long schedule of excavation and construction would disrupt a compact residential area that already feels beset by the hordes of tour buses that visit Washington National Cathedral, as well as the traffic and parked cars generated by NCS and the two other schools on the cathedral campus, St. Albans and Beauvoir.

Critics also say the above-ground portion of the field house and the extension of a wall along Woodley Road would dominate the view of the cathedral grounds and the cathedral from 34th Street NW and neighboring streets.

Attempts to negotiate a smaller, less obtrusive facility with school and cathedral officials have been unsucsessful, said Edward J. Burger Jr., president of the National Cathedral Neighborhood Association, the group of homeowners who banded together this year to fight the project.

Berger, who lives across the street from the proposed field house, said he and other neighbors who oppose the plan felt "forced, I'm afraid, to go head-to-head with the cathedral and the cathedral school."

"We feel a bit saddened by the behavior of the cathedral," he said. "It's unfortunate this had to reach this temperature, and we tried early on to prevent that."

Responds school trustee Robert Carr, "We think we've been very responsive to everyone's concerns."

The field house and garage would be on 4.5 acres along 34th Street and Woodley Road NW, on the site of the school's existing playing field and tennis courts. The field house would contain an indoor running track, four multiuse competition-level courts, a 5,000-square-foot weight and training room, lockers and showers. Its roof would be sodded over and converted into a playing field.

The facility is intended, said NCS headmistress Agnes "Aggie" Underwood, "to meet the critical lack of athletic facilities available to our girls."

The school's current field and gym facilities -- a single gym, one multipurpose room, one playing field and seven tennis courts -- have been virtually unchanged since 1954, Underwood said. Almost all 400 students in grades 7 through 12 compete on one or more of 39 teams in 15 different sports. Yet NCS has no lockers and showers on site for its student athletes.

No one disagrees that NCS needs to update and expand its student athletic facilities. At issue, however, is how big an athletic facility is too big for 546 girls?

The opponents say the planned building is so large and comprehensive that it should be considered a stand-alone project, rather than essential to the school's curriculum, and thus be governed by special zoning regulations. They argue that, because the field house would be used by the community in the evening and weekends, it could be considered a community facility.

"This facility is so large it far exceeds any need of the school," said Tom Dernoga, one of the attorneys hired by the National Cathedral Neighborhood Association.

NCS attorney Whayne Quin calls that argument nonsense. The athletic program, Quin said in documents filed with the board, "is just as much a part of the school curriculum as mathematics, social studies, art, drama, etc."

Other neighborhood groups have tentatively supported the planned field house, but only if public use is limited. The school has agreed to the restrictions.

CAPTION: National Cathedral School headmistress Agnes "Aggie" Underwood and school trustee Robert Carr at the gym site.

CAPTION: At the gym site, National Cathedral School headmistress Agnes "Aggie" Underwood and school trustee Robert Carr talk about the proposal.

CAPTION: The school's proposed field house and garage would replace existing tennis courts and a playing field.