Back when he was Montgomery County executive (1994-2006), Doug Duncan was widely regarded as a go-to-guy for the business community. He led the revitalization of downtown Silver Spring and pushed hard for the Intercounty Connector. His “End Gridlock” slate of candidates in 2002 proposed nearly 60 miles of new roads.

It’s a record that didn’t endear him to environmentalists, who saw him as a public official who never met a slab of concrete he didn’t like. His subsequent private sector career, which has included consulting gigs for the Lerner family and Foulger-Pratt, has only added to the perception.

But Duncan, running for a return to office in the June Democratic primary, was as green as a leprechaun’s coat Wednesday when he announced his solidarity with environmentalists who want to protect northern Montgomery’s Ten Mile Creek watershed from new development. The area, which includes the town of Clarksburg, is the site of a huge land use fight over proposals by two major developers — Pulte and Peterson-- to build new homes and retail.

“The Creek is like an endangered species — we value it for many reasons,” Duncan said in a statement that went up on his campaign site and out through e-mails. “If we destroy it, we will learn, to our regret, that it was truly irreplaceable.” He called for a “policy of no further degradation” of Ten Mile Creek.

Last summer the Montgomery Planning Board staff recommended an amendment to the Clarksburg master plan to sharply limit new construction in the area. The Planning Board adopted a less restrictive blueprint that is now pending before the County Council. It is expected to take a final vote sometime next month.

“I think they need to drastically reduce what planning board and staff recommended,” Duncan said in an interview Wednesday.

Asked how he reconciles this stance with his prior record, Duncan said he doesn’t need to.

“I am still very business-friendly and will be a very business-friendly county executive. We need economic growth in the county,” he said. But he added, “We made so many trade-offs for our waterways in our county. Let’s save it [Ten Mile Creek]. Protecting it is not going to make or break Montgomery’s economic future.”

Duncan’s declaration places added pressure on County Executive Isiah Leggett, who is seeking a third term, to stake out a strong anti-development stance.

He told members of the Save Ten Mile Creek Coalition at a meeting earlier this month that the county was prepared to forego a proposed addition to the County Correctional Facility in Clarksburg (a site selected on Duncan’s watch) and another 128-acre county-owned parcel in the watershed.

But on the Pulte and Peterson projects, Leggett said he wasn’t ready to take a position. He said he is working on trying to bring the sides together.

“We are hopefully trying to work on some kind of consensus,” he said. “I just think we should let the process play out a little.”

Council member Phil Andrews (D-Rockville-Gaithersburg), the other primary contender, who also opposes the current plans for Ten Mile Creek, said he welcomed Duncan’s support.

“I would have liked to have seen him testify at the public hearing,” Andrews said. “But I’m glad he’s on board.”

During Duncan’s third term, building irregularities and botched oversight made the new town of Clarkburg a code word for development run amok.

But Upcounty activists also embraced Duncan’s advocacy, even if it meant giving him the benefit of the doubt. Caroline Taylor, executive director of the Montgomery Countryside Alliance, said Duncan had clearly “taken the political barometer “ on the issue but had also done his homework.

“We are grateful for support from any segment whatever the motivation, altruistic or otherwise,” Taylor said.