As spectators trickled into the Robert Trent Jones Golf Club in Gainesville yesterday to watch practice rounds of the prestigious Presidents Cup tournament, Prince William businesses and government officials prepared for what will likely be the best week for the county's economy all year.

The tournament, which is making its fourth appearance at the exclusive private club, is expected to draw 20,000 visitors a day and could generate $5 million to $10 million for the county's economy, said Sean T. Connaughton (R), chairman of the Board of County Supervisors.

"There isn't a single hotel room in western Prince William," he said.

Businesses have beefed up their staffs, and the bill for the county, the city of Manassas and the visitors bureau for advertising, traffic control and other services for the golf club and the Professional Golfers' Association will come to about $700,000.

The zip of credit cards sliding through charge machines means tax revenue will easily top that figure, officials said. But it is the intangible payback that most officials and business owners are counting on from the thousands of spectators and hundreds of journalists from all over the world who will be talking about their visit -- through the media and by word of mouth.

Prince William boosters will use this week to sell the county as a year-round tourist destination and a great place to live and work. With its fast-growing population and increasing wealth, the county will try to show the world that it is a premier place to golf and live the good life, Connaughton said. "Hopefully, [visitors] will walk away with a positive impression of the county and our businesses," he said.

And businesses are doing boffo. Many restaurants in prime locations near the course off Route 29 did not exist five years ago, when the tournament was last held in Prince William. They're hoping to attract much more than their usual clientele of newcomers to the neighborhood's high-end subdivisions.

Bonaventure Gonsalves, a managing partner of the Bonefish Grill in Gainesville, said he had contacted another Bonefish Grill in Southern Pines, N.C., where the U.S. Open Championship was played in June, to get an idea of what's in store and how to prepare.

"I just ordered more of everything," he said, even extra chairs.

The restaurant, which usually closes at 10 p.m., is staying open until 1 a.m. starting tonight, Gonsalves said.

The Brass Cannon Restaurant at Stonewall Golf Club is retooling for expected walk-ins from the Presidents Cup gallery. "We've taken the menus out of play, and we're creating elaborate buffets. Fruit and cheese towers, carving stations," food and beverage director Tim O'Meara said.

The Prince William County-Manassas Convention Bureau is hosting a half-dozen tour operators who specialize in selling golf trips, hoping they will be so impressed that they will include Prince William, with its 12 daily-fee courses, as a vacation stop, said Tabatha Mullins, the bureau's executive director.

Just about everyone in county government is focused on the tournament this week. The Board of County Supervisors canceled its meeting Tuesday night to attend a reception at the event. The convention bureau, which has spent about $300,000 promoting the Presidents Cup, is set up at the tournament and has information tables at all 35 hotels in the city and county, Mullins said.

Hotel revenue for the month that included the 2000 Presidents Cup was up 32 percent, or $1.2 million. The event helped boost hotel revenue for that year by 25 percent, Mullins said. And with the Prince William rooms tax of 5 percent, that kind of surge in business will translate directly into more revenue for the county.

The extra money will more than cover the 90 police officers and sheriff's deputies who are directing traffic along congested Route 29, just off Interstate 66, Assistant County Executive Susan Roltsch said. She said an undisclosed number of officers also will provide security to players and will assist in the protection of dignitaries, including former presidents George H.W. Bush and Bill Clinton, who organizers said are scheduled to attend the first day of play today.

About $40,000 has been set aside for overtime for officers, but the cost may be higher, said Liz Bahrns, a county spokeswoman.

The county has waived $81,000 in permit fees at the golf club, where organizers built an eight-bedroom cottage for players and created a small town of two dozen tents.

Manassas spent $25,000 to produce 50,000 bottles of water with the city's logo to serve as the tournament's official water, said Lawrence Hughes, the city manager.

The city, county and convention bureau also are working to quantify the true economic impact of the tournament, officials said. Debi Sandlin, economic development director for Manassas, will do much of the math.

Her position did not exist in 2000, so the city had no one to calculate the tournament's costs or benefits to the little city five miles from the Robert Trent Jones course. She said she will compare sales taxes from this week to the same week last year to get an idea of the tournament's effect.

The city particularly focused on advertising Manassas Regional Airport as more convenient to the golf venue than Dulles for spectators arriving by private plane.

The convention bureau used hotel revenue as its main gauge of economic impact in 2000. This time, it will survey restaurants and other businesses as well, Mullins said.

Ajay Kapur, general manager of the Holiday Inn Manassas Battlefield, said the tournament has brought the 158-room hotel its best business by far this year. "We have been booked for two weeks with people working the tournament and spectators," he said. "We need to have more events like this."