After four years of study and $4 million, the favored route for a tri-county parkway -- a proposed highway that would connect Prince William, Loudoun and Fairfax counties -- is unlikely to get the federal funding or the approval it needs to be built as it is currently proposed, said Ken Wilkinson, project manager for the Virginia Department of Transportation study.

Wilkinson said that the U.S. Army Corps of Engineers looks for roadways that cause the least disturbance to the environment, and that the route favored by 40 percent of the public -- as determined through e-mails, letters and surveys -- is not the best of four proposals.

Wilkinson explained the Corps' conclusions at a recent meeting of the Prince William Board of County Supervisors. Supervisors expressed frustration that the route the public wants and that all three counties already have in land-use plans is no longer an option.

At its meeting Monday, the Fairfax County Board of Supervisors is scheduled to consider endorsing a route. The county's business leaders generally back the same route as Prince William officials. The policymaking Commonwealth Transportation Board wants to hear the preferences of local officials by November.

The favored route is known as the Comprehensive Plan Alternative because all three counties have placed similar routes in their land-use plans. It is also the most expensive, at $548 million, and would wind 11.7 miles from Route 50 near Dulles through a bit of Fairfax County in Bull Run Regional Park and east of the Manassas National Battlefield Park, ending at the Route 234 bypass and Route 28 interchange in Prince William County.

In a June letter to the Federal Highway Administration, Nicholas L. Konchuba, chief of the Eastern Virginia Regulatory Section of the Corps, wrote that building the road would require a permit from the Corps because it would "involve impacts to waters of the United States, including wetlands."

Because the path's potential impact on wetlands and streams is greater than the other proposed routes, the Corps would likely not issue a permit for construction, Konchuba concluded in the letter, of which supervisors received a copy.

"This damn thing was on our comp plan for 30, 40 years," board Chairman Sean T. Connaughton (R) said after Wilkinson's presentation, adding that the proposal is now off the table.

Wilkinson said there might be hope, noting that Route 288 around Richmond had similar obstacles but was constructed.

"Mr. Wilkinson, I appreciate you being here. I don't appreciate the message," Connaughton said.

The Northern Virginia Transportation Alliance, a Fairfax-based nonprofit coalition of businesses and citizens, said that despite Wilkinson's comments, "nothing said or implied by any federal or state agency definitely rules out tri-county parkway construction along the route favored by local governments for a decade or more."

The alliance said in a statement: "What the Federal Highway Administration and Army Corps of Engineers did say was that portions of the Comprehensive Plan Alternative may not be eligible for federal funding."

Stewart Schwartz -- executive director for the Coalition for Smarter Growth, which has staged several protests against the multimillion-dollar roads -- said, "They are wasting our tax dollars by studying and pushing these bypasses."

The best alternative is to focus on creating interchanges at Route 28 and Interstate 66 that could help ease traffic, he said.