Legal and political tensions surrounding development in Clarksburg have risen to the point that Montgomery County Council members have been told by their attorney to exercise caution in what they say about proposed revisions to a land-use plan they will consider next month.

The admonition came after Pulte Homes served notice that it would sue the county if it was prevented from building hundreds of houses in the environmentally sensitive Ten Mile Creek watershed in the Clarksburg area.

Meeting in closed session Tuesday, council members and staff were warned not to say or write anything publicly or privately implying that politics — rather than policy or environmental science — might enter into their deliberations, according to three people in the meeting who spoke on the condition of anonymity because they were not authorized to speak publicly about the matter. Such statements, they were told, could be used in court to undermine the county’s legal position if Pulte filed suit.

Members were also asked not to delete or destroy any communications regarding the matter.

“If Pulte can prove that the council has acted politically, rather than on the merits, it will strengthen them in court,” one of the attendees said.

Cathy Wiss, coordinator of the water quality monitoring program at the Audubon Naturalist Society, collects samples in Ten Mile Creek this past summer in Clarksburg, Md. She and others are advocating for the full preservation of the Ten Mile Creek watershed. (Katherine Frey/The Washington Post)

The attorney’s warning underscores the high stakes over the future of Clarksburg. The northern Montgomery community was once envisioned as a transit-friendly suburb with a green, walkable village at its heart. A series of setbacks over the past 20 years — a sour economy, unfulfilled commitments by developers and transit plans that exist only on the books — have left Clarksburg short of that vision.

Environmentalists have framed the issue of new construction in Clarksburg as a defining moment for council members, who face reelection in 2014. They have urged members not to seek a false “balance” between economic growth and environmental protection. Pulte, meanwhile, has asserted that the county could jeopardize an investment of tens of millions of dollars.

The amendments would limit development called for in a 1994 master plan for Clarksburg. The zoning in the original plan would allow Pulte, a giant national home builder, to construct about 1,000 single-family homes on a 538-acre rural expanse it owns west of Interstate 270 between Shiloh Church and Clarksburg roads. Pulte spent $46 million for the land and an additional $11 million for development rights from landowners in the Agricultural Reserve. The transaction was made under a county program designed to preserve the farmland in the reserve while allowing more construction in selected areas.

But the 1994 plan also called for a review of the watershed’s health before development entered the final “build-out” phase, which would include the Pulte project. Last fall, the council asked the county Planning Board to take another look at the master plan. Studies showed that polluted runoff from exiting development had damaged water quality and that it would continue to deteriorate if construction went forward as originally allowed. Ten Mile Creek is a tributary of Little Seneca Reservoir, water from which could be released into the Potomac River to bolster the water supply in the event of drought or other emergency.

In July, the Planning Board staff recommended limiting Pulte to about 200 homes, with much of the rest of the site set aside as permanent open space. The board voted in October for a considerably smaller reduction, allowing about 500 homes, though most of those would have to be townhouses, not single-family houses.

Pulte wants something close to the original master plan. In a Dec. 3 letter to the council, Pulte attorneys Gus Bauman and Robert Harris said the proposed revisions violate the company’s constitutional and property rights and amount to “death by a thousand cuts.”

Among the contested provisions is one that would bar Pulte from turning more than 10 percent of its site into impervious surface (such as driveways and roads) that would increase runoff into the creek. The attorneys called the Planning Board’s action “discriminatory,” noting that the board granted Peterson Cos., which is building a mixed-use project east of I-270, a 25 percent impervious-surface limit.

It also protested the “substantial and unwarranted” down-zoning of Pulte’s land from a density of two homes per acre to one unit per five acres.

“The harm to Pulte is in the tens of millions of dollars,” Bauman and Harris said. “We ask that you avoid these results by reconfirming the current Master Plan and zoning.”

According to attendees of Tuesday’s meeting, the council’s senior legislative attorney, Michael Faden, described Pulte’s case as not particularly strong. He said the county was not worried about defending the council’s decision as long as the issue was seen as having been decided on the merits.

“They don’t seem concerned about it,” one official said. “If Pulte were to prevail, it would mean the council would never be able to down-zone.”

Bauman said Thursday that the letter speaks for itself. “We stand by the letter,” he said.

Faden declined to comment Thursday. “I can’t talk about that,” he said.