Proposals to limit development in Clarksburg’s Ten Mile Creek watershed cleared a major hurdle Tuesday, as two Montgomery County Council committees agreed to cap the amount of impervious surface produced by new construction.

A series of votes by the planning and transportation committees — after weeks of scientific briefings, closed-door conferences with attorneys and intense lobbying by environmental activists — sets up final action by the full council before the end of the month.

Tuesday’s session all but concludes a 16-month debate over where and how the northern Montgomery town of Clarksburg will grow. Scientists made clear that only zero growth would guarantee the health of Ten Mile — one of the county’s last clean, biologically robust creeks. But the zero option also would have landed the county in court, officials said, where it would have to defend stripping land owners of their property rights.

“The bottom line,” senior legislative attorney Michael Faden said, summarizing admonitions delivered to the council in closed session last week, “is that whatever regulations the county imposes have to leave some economically viable use of the property.”

In the end, council members tried to craft a plan to allow some construction, to foster the evolution of Clarksburg and limit damage to the watershed.

“Nothing’s perfect, but this is clearly a really good decision,” said council member Marc Elrich (D-At Large), a member of the planning committee.

The committees’ actions focused on three properties slated for development, and set limits of 6 percent impervious surface on one site and 15 percent on the other two. The so-called “6-15-15” scheme, proposed by County Executive Isiah Leggett, was a shift from a measure promoted last week by Elrich and two other members, Roger Berliner (D-Potomac-Bethesda) and Hans Riemer (D-At Large), to limit impervious surfaces to 8 percent limits for all three properties.

Leggett aides, backed by testimony from University of Maryland environmental scientist Matthew Baker, said streams in excellent health are especially sensitive to even minute environmental changes, while portions of the watershed already somewhat degraded by construction can more easily absorb more development. Lowering imperviousness on the Pulte Homes site from 8 percent to 6 percent would enhance protection of some of the watershed’s cleanest stream segments, they said. A higher percentage would do relatively less damage on portions of the watershed to the east of I-270 that have already been impacted by building.

Pulte planned 800 houses or townhouses on 538 acres west of I-270 between Shiloh Church and Clarksburg roads.

County officials and environmentalists said building 800 homes posed a threat to Ten Mile, in the form of polluted runoff from new expanses of concrete. Ten Mile Creek is one of several tributaries of Little Seneca Reservoir, part of the region’s emergency water supply.

The five members of the combined committees voted to cut Pulte’s footprint by roughly half, reducing the amount of permissible impervious surface from 12.5 percent to 6 percent of the site. Depending on how homes are clustered, it would allow between 200 and 500 units of housing. Pulte, which has threatened to file suit if its plans were limited, expressed disappointment Tuesday.

“This decision, if enacted, is a serious setback not only for the Clarksburg community, but for us and others considering doing business in Montgomery County,” Lewis Birnbaum, president of Pulte’s Mid-Atlantic division, said in a statement.

Diane Cameron, director of conservation programs for the Audubon Naturalist Society and a leader of a coalition opposed to development in the watershed, said the group “remains committed to full protection” of Ten Mile Creek. But Cameron added that environmentalists are nevertheless heartened by the proposed caps on imperviousness.

“We appreciate that the council heard the people’s call,” she said.

The committees voted to recommend a 15-percent imperviousness cap on two properties east of I-270, closer to the Clarksburg Town Center. On one site, Peterson Companies proposed 450,000 square feet of retail and a 250-room hotel, a plan that would have left 35 percent of its site with impervious surface. Last summer, the county planning board recommended whittling the project to 25 percent imperviousness. The committees settled on 15 percent, saying they were willing to allow higher density than on the Pulte site because the Peterson site was near stream segments already damaged by past construction. One member, planning committee chair Nancy Floreen (D-At Large), dissented, favoring 20 percent imperviousness.

No one was completely satisfied by the final outcome. Keith Van Ness, the county’s senior aquatic ecologist, called it “ the lesser of two evils,” a description that drew a sharp response from Council President Craig Rice (D-Upcounty), who represents Clarksburg. Rice said that facilitating the construction of places for people to live and work did not constitute an evil.