The last segment of the Great Seneca Highway in upper Montgomery County will open today, marking the end of a decade-long battle over the largest highway project undertaken by the county.

The final 3.2-mile stretch of the eight-mile, four-lane highway sparked a protracted struggle that pitted county officials against environmentalists and citizen groups who opposed its construction near houses and through 22 acres of park land. More than 40,000 vehicles a day are expected to use the road. The $47 million highway snakes from Middlebrook Road to Route 28.

According to county officials, the highway was built to relieve pressure on the heavily congested Interstate 270 corridor and provide a vital link between the expanding subdivisions of Germantown and employment centers in the Rockville area.

"I'm very proud that we were able to finish it," said Montgomery County transportation director Robert McGarry. "It's a good-looking road, and it meets our commitment to Germantown in making it a corridor city."

But, John Walker, president of the Quince Orchard Valley Citizens Association, said the county ignored the harm the road will do to Seneca Creek State Park.

"I feel the county has really forced this particular {road} no matter what the environmental cost, because it was the easiest way out," he said. "I still don't like what it has done to the park."

According to County Engineer Edgar Gonzalez, "The key issue was not whether we would cross the park. The key issue was where was the best place to cross the park."

The final link runs from Dairymaid Drive, just south of Route 117, to Quince Orchard Road in Gaithersburg.

The other two links, from Middlebrook Road to Clopper Road and from Route 28 to Route 124 have been open for several years.

A vocal coalition of environmentalists and civic groups fought the building of the road for more than 10 years, arguing that it would damage one of the region's largest wilderness areas.

The Department of Interior initially opposed the project in July 1985, but approved it in June 1987 after the county agreed to erect sound barriers, build bridges so wildlife could cross below safely and buy replacement land for the woods the road would destroy.

Nine months after the federal government granted permission for the county to build the highway through the park, the Quince Orchard Valley Citizens Association and the West Riding Citizens Association sued in March 1988 seeking to block construction. The groups lost their suit, but the county agreed to landscape along those parts of the highway near houses.

Louis Greene of Quince Orchard Valley lives 75 yards from the highway. During winter, he can see the highway from his back yard.

His biggest complaint is that rainwater from the highway berms often flows into his back yard. The highway is "not really quite as bad as I thought it would be," the 37-year-old police officer said.

County officials and environmentalists agree that the highway will have some adverse effects on wildlife in the state park.

According to park manager Cliff Denney, the road has already affected wildlife migration. And he anticipates more deer kills after the road is open to traffic.

But the naturalist said he thinks the Great Seneca Highway and the "little critters," as he referred to the racoons, skunks, deer and foxes that inhabit the region, can coexist.

"I don't think anyone wants to trade off people for wildlife," Denney said. "We're going to have to provide for people and salvage as much of the resources as we can."

Staff writer Stephen C. Fehr contributed to this report.