A proposal by D.C. government planners to create a special buffer between downtown offices and adjoining residential neighborhoods has been sharply attacked by community activists who fear that it would promote further commercial expansion in their areas.

The special buffer district is part of the city's draft comprehensive land-use plan and would permit commercial and residential units to coexist along a strip one and two blocks wide, bordering downtown. The buffer would run roughly along New Hampshire Avenue NW to Dupont Circle and down Massachusetts Avenue NW to about Third Street NW. Precise boundaries have not yet been determined.

"A lot of us are tired of fighting," said Joseph N. Grano Jr., president of the Dupont Circle Citizens Association. Grano said that the proposed buffer zone would not stop commercial encroachment and might actually be worse than current rules.

"You're just creating a situation where you're perpetuating flux, and that's not what we should expect, living in residential neighborhoods," Grano said.

City planning officials said that the proposal is an attempt to strengthen present zoning regulations, which have proven largely ineffective in preventing commercial encroachment into residential neighborhoods such as Dupont Circle.

In addition, officials said, they want to provide adequate commercial space in the near dowtown area for offices and businesses that cannot afford high office rents in more centralized downtown locations.

"The city can't be in a position to say, 'If you can't pay rent downtown forget it,' " said John (Skip) McCoy, director of the city's planning office, at a meeting of Ward 2 residents Thursday evening. "That's not realistic, looking at population projections and the way the town functions economically."

White-collar, service businesses such as trade associations, law firms, think tanks and other information-gathering groups form a major segment of the city's business economy. Many of those firms find the adjacent downtown areas, such as Foggy Bottom and Dupont Circle, attractive locations, sparking the commercial encroachment that has the citizens' groups up in arms.

Grano and community activists from Logan Circle, Foggy Bottom and other neighborhoods said that, instead of a buffer district, the city should adopt a policy that would set up specific residential and commercial zones.

The buffer proposal now under discussion is separate from city zoning regulations and, if approved, would become part of the city's proposed land-use plan. The plan is to be used as a guide to future zoning regulations, but specific ways in which the regulations would be changed to conform with the plan have not been determined.

Present zoning regulations include a similar buffer zone, called "Special Purpose," that permits some commercial development such as law offices and trade associations in approximately the same area covered by the new proposal.

McCoy said the new plan provides greater protection for neighborhoods because it specifies that residential development is the preferred use for the areas north of Massachusetts Avenue near Dupont Circle and west of New Hampshire Avenue near Foggy Bottom and West End.

The proposed buffer district and the comprehensive plan will be discussed at a conference sponsored by citizens' groups at the District Building today, from noon until 5 p.m.