The White House advance teams started their invasion more than a month ago, occupying the College of William and Mary's Campus Center, expelling the students and forcing the relocation of the senior dance. Last week, the helicopters began swooping down upon the town's restored colonial village while caravans of black limousines cruised its streets in dry-run rehearsals.

"A lot of people are getting kind of tired of all this," said Ryan Fletcher, a shopkeeper in the village who was dressed in his usual costume of wig and breeches. "It's sort of difficult to create an 18th century setting with all these helicopters flying around."

The airborne intrusion is only one of the irritants as planning for the ninth Summit of Industrialized Nations reaches its crescendo. By the time the festivities begin Saturday, more than 1,500 diplomats and support staff and as many as 4,000 journalists are expected to show up for a three-day international extravaganza whose cost is estimated at $7 million.

The White House, which has solicited tax-deductible donations for the affair from more than 100 companies, is calling it a showcase for President Reagan's private-sector initiative. The Colonial Williamsburg Foundation--the Rockefeller-founded organization that operates the restored Virginia colonial capital and has received a $1 million contract to handle the summit--is officially bullish, hoping to profit from the worldwide publicity the event will generate.

"This is the most complex and prestigious thing to happen here since they signed the Virginia Declaration of Rights in 1775," said Albert O. Louer, the foundation spokesman.

But not everybody here is so excited about all the commotion. The elaborate arrangements--including the installation of 600 telephones and 25 miles of cable--have disrupted life in this small Tidewater community, driven away some of its tourists and annoyed many of its residents.

"It's grandiose, its a show," said Martin Moorefield, a local hotel manager who was less than impressed with the results of last year's summit in Versailles and the 1981 gathering in Ottawa. "What benefits have there been from the last two summits?"

Most of the irritation, however, is directed not so much at President Reagan and the leaders of the six other industrial democracies that will gather here, but at the hordes of journalists who are expected to take over the town and share in the summit extravagance. In fact, officials acknowledge, a large part of the summit budget is devoted to the care and feeding of an international press corps that will outnumber summit participants by better than 2 to 1.

At a cost of more than $1 million, William and Mary's basketball arena has been converted to a lavishly decorated International Press Center that will provide free typewriters, computer terminals, telephones and telex service for the journalists. Gold carpeting has been laid over the gymnasium floor, blue and white drapes have been hung from the ceilings and a new central air-conditioning system has been installed, thanks to 50,000 feet of electrical wiring.

"It's absolutely ridiculous," said Bucky Walters, a tourist from Gloucester, Va. "I'm sure all the hard-working students at William and Mary can make do without central air conditioning. I think everyone's coddling to the media."

The air-conditioning system, however, only begins to touch on the amenities available to the visiting press corps. There will be a post office, a currency exchange desk and a travel agency inside the press center and a 24-hour shuttle bus service to take them to it. Outside the hall, a one-acre canvas tent stocked with exclusively American cuisine will offer what one summit spokesman calls "continuous" free food service.

Encouraged by White House promises of tax breaks and the prospect of good public relations, more than 65 firms have donated foods for the press tent, including 2,300 pounds of chicken and 1,800 pounds of Cornish game hens. Granny Good Foods of Oakland, Calif., has supplied 1,020 bags of Hawaiian-style, extra-thick potato chips and Benzel's Bretzel Bakery of Altoona, Pa., has shipped in 1,296 bags of pretzels.

Anheuser Busch, Stroh's and Coors will offer kegs and trucks of beer on an "as-needed basis," another spokesman says. California wine companies have donated 120 cases of wine.

To be sure, none of this compares to the menus of Alaska king crab, Maine lobster and American caviar that have been devised for the heads of state by Craig Claiborne, The New York Times food critic who is serving as a consultant to the summit. But the job of obtaining enough food to feed the press corps has exasperated summit planners nonetheless.

"It's unfortunate," says Michael A. McManus, who as summit administrator has been in charge of making arrangements for the journalists. "I don't think summits were ever intended to require this kind of role in terms of support for the press, espcially since they the reporters are all on expense accounts. But somehow it has evolved that way."

The larger question for many, however, is exactly what the journalists are going to have to write about. The summit is supposed to map out a strategy for world economic recovery. But all the plenary sessions--along with the evening banquets at a nearby plantation Saturday and the restored Royal Governor's Palace on Sunday--will be conducted in private. The only official event open to the media will be President Reagan's reading of a joint communique, to take place in the press center from 3 to 3:10 p.m. Monday, according to the official summit schedule.

The expectation that many of the journalists will be doing a lot of idle wandering has prompted Colonial Williamsburg to instruct its employes to show up for work in their 18th century costumes, even though the village itself will be closed to the public for the first time in its 57-year history. Meanwhile, the state of Virginia has decided to vie for their attention by setting up a tourism booth in the press center.

"The state is hoping that while some of the journalists are sitting around waiting for briefings they will write sidebars about Virginia Beach or other tourist attractions," said George Stoddart, press secretary to Gov. Charles S. Robb.

The occupation of Williamsburg had once instilled fear among local merchants and innkeepers, who worried that the closing of Colonial Williamsburg combined with tight security surrounding the summit would scare off tourists. But the Innkeepers of Williamsburg, a local trade association, counterattacked by launching an East Coast advertising campaign promoting Dick Clark's "Good Ol' Rock N' Roll Show," also scheduled for this weekend at nearby Busch Gardens.

The Busch Gardens crowd, combined with the journalists who have taken out rooms at most of the town's larger hotels, appears to have alleviated much of the early concern. But some of the smaller motels, shunned by the journalists, are still empty and are having trouble attracting tourists frightened off by the summit publicity.

Norma Crammer, owner of the 21-room Ironbound Inn, said last week that she was still one-third empty for Memorial Day. "I've been entertaining the idea of sending the White House a bill for the empty rooms."