When Fairfax County decided to restrict smoking in restaurants, business persons braced for the worst: Empty tables in no-smoking sections; costly renovations to comply with the new law; county health inspectors watching intently for errant diners to light up.

But after living with the regulations for seven weeks, many once-skeptical restaurant operators are surprising even themselves with their reaction. They say that it has been easy to implement and that their customers are enthusiastic about the law.

"We're constantly amazed at how successful it has been," said Noel Panella, assistant general manager at Clyde's of Tysons Corner. "The nonsmoking rooms are continually full, and the clients are very happy. It's really proved a point to the restaurants in that it has presented no problems.

"At first we were very leery about it," Panella said. "We were afraid it would cut down on our flexibility and hurt business."

The law, enacted by the Fairfax County Board of Supervisors by a one-vote margin in December, requires restaurants with a seating capacity of at least 100 to set aside 25 percent of their dining space for nonsmokers. Restaurant operators who fail to comply are subject to a $25 fine each time they are found to be in violation.

Individual diners also can be fined $25 if a county inspector finds them smoking in a restricted area.

Since the law went into effect on March 1, no fines have been levied, according to the Fairfax County Health Department.

Gregory T. Farrell, manager of Chi-Chi's restaurant in Springfield, applauds the regulation. "I think it has helped business. People really appreciate that we offer it," he said. "We have proven all the doomsayers wrong."

Despite the acclaim, the potential for a challenge still exists. In urging the supervisors to reject the law, restaurant and tobacco industry officials condemned it as an example of government intrusion and threatened to fight it in the courts.

James M. Wordsworth, president of the Northern Virginia chapter of the Virginia Restaurant Association, said the group is still evaluating the situation.

"If you allow this to happen, then what's next?" said Wordsworth, who is the manager of the J.R. Stockyards Inn at Tysons Corner. "We're more concerned that it's going to open the gates," prompting additional regulations.

In sponsoring the ordinance, Fairfax Supervisor Thomas M. Davis III (R-Mason) insisted that it was not aimed at limiting the freedom of smokers but rather at recognizing the rights of nonsmokers.

For many restaurants, particularly large ones such as Clyde's, Chi-Chi's and the Chesapeake Bay Seafood House, adhering to the law has meant simply reserving separate dining rooms for smokers and nonsmokers. Smaller restaurants have been urged, where possible, to use physical barriers such as planters or screens.

Mark G. LaCroix, a senior inspector in the Fairfax County Health Department, said the level of compliance has been very high. "We haven't had any difficulty in getting anyone to comply," he said, adding that the county has received only about a half-dozen complaints from nonsmokers about possible violations and that those restaurants complied after being told of the regulations.

County officials estimate that 150 to 200 of the approximately 1,650 food establishments scattered throughout Fairfax fall under the law, the only one of its kind in effect in Virginia.

Newport News enacted a similar ordinance in 1978, but the Virginia State Supreme Court overturned it a year later on appeal by a restaurant owner. Unlike Fairfax's law, however, the contested ordinance in Newport News did not establish a set number of seats to be reserved. Some restaurant owners reacted by reserving one or two seats in the middle of crowded, smoke-filled restaurants.

In its decision, the state's high court ruled that the ordinance as written was unworkable, according to Leonard A. Wallin II, an assistant city attorney in Newport News. The court "did not say the ordinance was unconstitutional," Wallin said.

No-smoking laws in the Washington area are in place in the District, where smoking is banned in public gathering places but is not restricted in restaurants. The Montgomery County Council has prohibited smoking in public areas and in commercial establishments, but it exempted restaurants after many restaurateurs promised to provide no-smoking sections.

One of those who initially had reservations about the Fairfax ordinance is Douglas T. Wilson, manager of Charley's, a 185-seat restaurant on Old Keene Mill Road in Springfield. Wilson said he and others were concerned about the potential costs of installing ventilation systems and erecting barriers, as well as with the prospect of long lines of patrons waiting for seats to open in the smoking sections.

"It's really not as bad as some people thought," Wilson says now. "We have separate dining rooms, so there has been no problem whatsoever."

At Chi-Chi's in Springfield, Farrell said, the public response has been so positive that owners of the Mexican-American restaurant have reserved 65 percent of the 480 seats for nonsmokers. Farrell said that officials of the nationwide chain have recognized for several years the popularity of no-smoking sections and had established nonsmoking areas well before the county's action.

He said the law should not be "that big of an ordeal" for restaurant operators. "It makes operating your dining room a little more of a challenge," he said, but he added, "It's not an unreasonable demand."

At the Chesapeake Bay Seafood House in Tysons Corner, initial concerns about the ordinance also have vanished. But William R. Easby-Smith, the restaurant manager, said he still objects to the government's self-imposed role in his business.

"I've been doing it all along," Easby-Smith said of the no-smoking sections. "I'd just rather have the flexibility to continue doing it for my customers without the county's interference."

Easby-Smith said he dislikes the idea of posting signs throughout the restaurant warning of the no-smoking law and listing the fine.

Herbert J. Clegg, vice president of the Richmond-based Virginia Restaurant Association, said restaurants should be left to establish their own no-smoking areas as business dictates.

"It should be the customer who guides the decision of the restaurant owners," Clegg said. "If the customers demand it, he'll do it or he won't be in business. Our big objection is that local governments are telling a man who has got to make his bread and butter from a business how to run that business."

"There are some things that should be reserved for business judgment, and this is one of them," added Wordsworth. "This breaks that thin line covering what should be done legislatively and what should be left to the businessman."

Wordsworth said that although members of the association's Northern Virginia chapter have discussed the possibility of a court challenge, "We're not that sure what we will do." He said an alternative would be to urge the county board to ease the 25 percent requirement, allowing owners greater flexibility in establishing how much space should be reserved for nonsmokers.

Meanwhile, individual restaurateurs appear to have accepted the law. "All of the feedback I'm getting from people in the restaurant business seems very favorable," said Panella, of Clyde's. "The managers are amazed at how full their restaurants are."