Gov. Robert L. Ehrlich Jr. (R) announced yesterday that Maryland wants to build an east-west highway across the Washington suburbs along a southern route that has been on planning maps for decades, despite the political, legal and environmental challenges that have dogged the project.

Standing on a grassy patch just south of the proposed route at Veirs Mill Road and Route 28, Ehrlich nodded to a small gathering of opponents and declared that "the vocal minority has won for too long. Today, the view of the vast majority finally wins."

Transportation Secretary Robert L. Flanagan said, "We will begin construction next year."

The 18-mile, $2.4 billion road, known as the intercounty connector, would be the most expensive new highway project in the Washington region and the first major road in the area in a generation. The six-lane highway would cut through a mixture of parkland and residential communities between the Interstate 270 and Interstate 95 corridors in Montgomery and Prince George's counties and claim approximately 58 homes in its path.

The communities along the chosen route include Shady Grove, Norbeck, Longmead, Drumeldra Hills and Fairland. The connector also would cross through Rock Creek, Northwest Branch and Paint Branch parks.

The "master plan" route selected by Ehrlich is the same one that was rejected by the federal government in 1997 as part of a required environmental review. The Environmental Protection Agency expressed concern that it would destroy parkland and wetlands, disrupt migratory birds and threaten a spawning area for brown trout.

Ehrlich said yesterday that the state would address those concerns by building bridges over sensitive areas, using advanced technology to manage storm water runoff and narrowing the road in some sections. State officials said they would also replace every acre of parkland with five acres elsewhere and spend $262 million to make environmental improvements in the areas around the highway.

The governor said, "We're confident this decision will be upheld by the federal government," which still must approve the project.

The state rejected an option that would have taken the highway north of Route 198, closer to Howard County, because it involved more significant environmental challenges and a greater impact on neighborhoods.

People who live along the chosen path in Montgomery said the selection of a route made the highway real for many who had been skeptical it would ever be built.

Amit Gessese, 44, said she and her husband, Yishak Tessema, 40, reviewed plans for the connector before they bought their townhouse in Longmead Crossing six years ago. But they weren't worried because planning officials told them, " 'It's not going to happen, because they've been talking about it for 20 or 30 years,' " Gessese said.

But Gessese said she has grown more concerned in the past year, as talk of building the connector intensified.

"We're not happy about it, but what can we do?" Gessese said. "It was a quiet, good neighborhood, but now we don't know what will happen."

The half-century history of the project has led many planners to doubt whether a road of this magnitude can be built in the rapidly crowding suburbs of Washington.

Other efforts to build highways, including additional Potomac River crossings and a north-south connector through Virginia's outer suburbs, have dissipated under public pressure and concerns about the billions of dollars it would take to complete them.

"This is truly a test," said Lon Anderson, director of public and government affairs at AAA Mid-Atlantic, which supports the connector. "Can we actually put major infrastructure in an already developed Washington area?"

Supporters say the highway is necessary to link the thriving business community that runs along I-270 with Baltimore-Washington International Airport and the Port of Baltimore, both accessible by I-95. They also say it would reduce traffic in the rapidly crowding northern suburbs.

Designating a route is an immense step for a project that was conceived in the 1950s as part of an outer beltway around Washington. As recently as 1999, the road appeared dead when then-Gov. Parris N. Glendening (D) canceled an environmental study because of concerns raised by local residents and the federal government about the highway's effect on streams, wetlands and wildlife.

But it gained a new life in 2002 behind the bipartisan support of Ehrlich, Montgomery County Executive Douglas M. Duncan (D) and several members of the Montgomery County Council, who all won election after making construction of the highway a central part of their campaigns.

The project got another jolt a year later when the Bush administration agreed to fast-track a required environmental review, shaving years off the process.

Bonnie Smith, spokeswoman for the EPA's mid-Atlantic regional office, said yesterday that the state's plans are a vast improvement over previous ones. "The State Highway Administration has made an earnest attempt to design a road which includes numerous features to avoid and minimize environmental impacts," she said.

Still, she said, there were concerns about the survival of the brown trout and other fish populations, echoing an agency report released in February that stated that "there is considerable risk that the trout population will be lost."

Despite yesterday's pronouncements, the road faces hurdles. The next step is for the federal government to approve a proposed route, a decision likely to come in the next few months. The state legislature could still balk at the project's escalating price tag, and opponents have promised to take legal action to stop its construction.

More than a dozen of those opponents served as a backdrop to yesterday's announcement, interrupting Ehrlich several times and carrying signs that included "The ICC Is Such a Scam. It Will Not Ease the Traffic Jam."

Highway opponents contend that instead of relieving traffic, a new suburban highway would spur more residential development that would beget even greater traffic problems. Opponents also charge that the road would one day become a link in an outer beltway that they say would lead to another generation of suburban sprawl.

They also say the environmental impact for a road that would slice through county parks, streams and wetlands would be too great a price to pay. They propose improving other roads, expanding mass transit and encouraging development closer to Washington.

"A majority of local road intersections will not see any change" in traffic, said Brian Henry of the Audubon Naturalist Society. "The public good is not being served here by Maryland's most expensive transportation project ever."

Montgomery County Executive Douglas Duncan, left, and Gov. Robert Ehrlich announce the route, which would pave over 58 houses as well as parkland.