Fairfax County will build a five-story, $35 million government center on Route 1, supervisors decided last night, combining social service agencies from more than a half-dozen locations and giving an economic development boost to the aging commercial corridor.

As part of the 30-year deal, a private company will build the South County Center and lease it to the county in exchange for the right to build a private office building nearby. Residents, social service providers and business owners hailed the unanimous decision, which came at 11:15 after a two-hour public hearing.

"It's one of the most remarkable, right things that government has done in my 12 years on the board," said Supervisor Gerald W. Hyland (D-Mount Vernon) after the vote. "It saves government tax dollars and makes us more efficient and, most importantly, allows us to better serve our citizens."

In other action, the county Board of Supervisors approved construction of a 10-field sports complex in Centreville.

Officials said the new Route 1 government center will offer one-stop shopping for most social services in the area, allow for the creation of a permanent center for seniors and teenagers and provide more space for badly needed services like dental and medical clinics, which now operate out of aging buildings.

They also said the government center will help revitalize the aging Route 1 corridor and save money by reducing the amount of office space the county rents. In today's dollars, county officials estimate the plan will save $17.9 million over 30 years.

Mark Sickles, the president of a nonprofit low-income assistance group called United Community Solutions, said building a government center in the area will help all the people his organization serves, many of whom are poor or elderly.

"Let's help our county employees be more productive," he said. "Let's reduce the burden on our working poor. Let's secure needed office space for 30 years and more. Let's take a few cars off the road. I thank you so much for your support of this win-win proposition."

Virtually all of the more than 100 speakers at the hearing supported the new center, saying it would make it easier for residents to receive services. After many people praised the project, dozens simply rose in their chairs to say "ditto" when their names were called.

Many of the speakers arrived at the board meeting on buses chartered by Hyland and Supervisor T. Dana Kauffman (D-Lee), who had planned to use county funds to pay for the buses and for box lunches for the many supporters.

Yesterday, under pressure from other supervisors, Hyland and Kauffman backed down and said they would pay the $500 cost of the buses and lunches from donations and their own pockets.

Critics had said they worry that the county is planning an overly elaborate facility. Many remember that the Fairfax County Government Center was harshly criticized as opulent when it opened in 1992. But only one or two speakers spoke against the proposal last night.

Several supervisors had initially questioned the financial wisdom of the deal, which allows a private developer to construct the building and lease it to the county. That deal also allows the developer, Madison Development Partners, to put a private office building on what is now county land.

Hyland, Kauffman and other county officials said that that part of the deal will be good for the area, where the commercial development is still dominated by fast-food restaurants, car dealerships, motels and run-down strip malls despite recent improvement.

In other action, young athletes in the Centreville area would have their own 10-field sports complex, dubbed the "Field of Dreams," under plans the supervisors approved despite objections from some residents who said the facility would cause too much traffic and noise.

By a vote of 9 to 1, supervisors agreed to allow the privately financed $20 million sports center, but only after its sponsors agreed to abandon plans for an outdoor amphitheater and for an indoor field house that would have included basketball courts. Citing concerns about safety on a nearby road, new supervisor Catherine M. Hudgins (D-Hunter Mill) voted no.

Representatives of the sports group that will pay for the complex declared victory after the vote. "I'm ecstatic at the fact that we got fields for our children," said Southwestern Youth Association President George Chernesky. "I'm a little disappointed at not getting the field house. But we'll take it one step at a time."

Chernesky said he has raised "not a dime" of the $20 million that his club will need to build the facility. But he said he is confident the club can assemble the money and build the complex within five years.

Opponents of the sports complex had told supervisors that the project, which is to be built in a rural part of Fairfax along a narrow road, would generate enough traffic to threaten the safety of the children who play sports there and those who live in nearby subdivisions.

They also had argued that noise from loudspeakers and lights from the fields would destroy the area's rural character. County planners had agreed with those concerns and urged supervisors to reduce the size of the original proposal.

Supervisor Michael R. Frey (R-Sully), who represents that part of Fairfax County, said the sports complex is necessary because there are too few fields to accommodate the tens of thousands of young people who want to play sports.

As a condition of last night's approval, the sports club has promised to make improvements to several parts of Bull Run Post Office Road.

And Chernesky said he is talking with state legislators to see whether money can be found to make more major fixes to the road. "Are we concerned?" Chernesky said. "You're absolutely right we are."