A generation ago, in a conference room in suburban Maryland, plans for an east-west highway were drawn. About the same time, a fisherman was squatting on the bank of Paint Branch stream, marveling over the first brown trout to be born in Montgomery County -- in a tranquil spot along the proposed highway's path.

It was the mid-1970s, a time when urban planners and ecologists dreamed big. In the 30 years since, the fortunes of the $2.4 billion intercounty connector and the humble brown trout have converged time and again. Twice, the trout won as environmental concerns trumped the highway project.

This time, with considerable political support and public sentiment behind the proposal, anglers and environmentalists said they fear that construction would destroy the habitat where the trout spawn naturally.

In the woods under a viaduct in eastern Montgomery, Nick Weber arched a hand-tied fly over clear waters yesterday and wondered whether the realization of one dream will mean the death of another.

"The fact that the fish can reproduce here says so much about the ecology in this region," said Weber, president of the Potomac-Patuxent chapter of Trout Unlimited, a conservation group.

"It's an indicator of the quality of environment that we have."

A day earlier, Gov. Robert L. Ehrlich Jr. (R) announced that the state had chosen a southern route for the 18-mile connector highway that would pass over the creek between Gaithersburg and Laurel, connecting Interstates 270 and 95.

Environmental activists, reluctant to give up their decades-long fight, said they are contemplating legal action if the Federal Highway Administration grants its final approval in the fall, as expected.

Advocates said they have spotted legal problems with the environmental study that was sped up and completed in 21/2 years -- about half the time such studies usually take. Ehrlich made a personal appeal to President Bush to put the study on the regulatory fast track.

That speedy review, advocates argued, led to a study that was too narrow and failed to consider other options for moving traffic through Montgomery and Prince George's counties more cheaply and without doing environmental harm.

Key to their consideration is the brown trout and parkland around Paint Branch that the Environmental Protection Agency has called "an unsurpassed natural resource in the region."

Across the country, activists have used litigation to stall such activities as logging and dam-building that could harm endangered creatures. But the brown trout isn't rare. It isn't even a native species.

Rather, the Paint Branch is the only stream within Montgomery County in which brown trout, introduced to this country from Europe in the late 1800s, reproduce naturally. Spring-fed, shaded and cleaned by trees on the protected land along its banks, the water is pure and cool enough to shelter a species and provide a recreational haven for a community.

"I'll bet this hasn't changed much in 30 years," Weber said. Looking at inch-long minnows darting around his waders, he said, "It would be tough to cross this stream off the list, when it was working. Really working."

The Paint Branch land was designated a special protection area by the county in the mid-1990s to provide for better environmental monitoring and strict controls on nearby development.

Environmentalists' worries are twofold -- first, that construction of the connector would foul the stream with silt, spills and debris; and second, that runoff from the highway would contaminate and heat the water, making survival difficult for the trout, which are highly sensitive to changes in their habitat.

In 1987, such concerns helped derail an environmental impact statement for the road. In late 1999, Gov. Parris N. Glendening (D) halted another study of the project, predicting that the connector would be an "environmental disaster."

State Highway Administration officials said they have built in sufficient safeguards for the trout, including a state-of-the-art filtration system to cool runoff water.

Planners also have proposed expanding bridges that ford the stream, which would add millions to the cost, agency spokeswoman Valerie Burnette Edgar said. "They are doing everything they can to avoid impacts," she said.

Environmentalists and anglers, though, argue that the state could have done more to improve existing roads or expand mass transit.

"They decided they were going to pour concrete as the solution, and they overlooked a whole bunch of options that cost less, are shown to be more effective in relieving congestion and have reduced environmental impacts," said Neal Fitzpatrick, executive director of the Audubon Naturalist Society.

If they pursue a lawsuit, advocates said, the first line of attack could be the premise of the environmental study, particularly its "purpose and need" statement, which declares the project is intended as a "state-of-the-art, multi-modal, east-west highway."

In a 2003 letter to the state, the EPA said it "accepted the wording" of the statement but noted that specifying the project as a "highway" narrowed the range of options. "EPA is concerned that [the statement] could infer a preference for one alternative," the letter said.

The EPA followed up in February with a letter stating that it favored the northern route, which it said would do less environmental damage than the route announced Monday.

Edgar said the state reviewed 3,500 submissions from government agencies and members of the public, including 8,000 different issues before choosing the highway route. She said the state expected lawsuits and could continue planning if a suit is filed.

Montgomery County Chamber of Commerce President Rich Parsons said opponents have not produced any options that would work better -- and that any legal action could add to costs if the project is delayed.

"It's a little frustrating because they generally lose these lawsuits," he said. "They've argued this for 40 years, and it's time for them to move on."

At the Paint Branch tributary, Weber cast a fly called a prince nymph and sighed. There's a chance the connector project again might be stopped, but he knows that's not as possible as it used to be.

Weber, a retired Food and Drug Administration biochemist, said he knows what it's like to commute, to rant in traffic -- and to come here for relief. Indeed, he said, the reason for the new road is also the reason for preserving the stream.

"Even with the cars there," he said, looking up at the viaduct, "There are moments when you don't hear them."

Nick Weber, president of the Potomac-Patuxent chapter of Trout Unlimited, is among those worried about the effect of the proposed highway on Paint Branch.