BEVERLY HILLS, Calif. (AP) _ Restaurateurs who convinced the City Council to weaken a strict four-month- old anti-smoking law said Wednesday they're pleased with the change and hope business will return.

The council voted 5-0 Tuesday night to relax the widely ignored ordinance, which had banned all smoking in restaurants except for those in hotels. Bar areas had been exempted under the law, regarded as among the nation's toughest.

Under the new rules, which took effect immediately, restaurants may establish smoking areas provided that air-filtering systems prevent any smoke from reaching no-smoking areas. Bars must also have air-filtering systems and designated smoking areas to appease non-smoking tipplers.

The change had been sought by most restaurant owners in this exclusive Los Angeles suburb, home to the swank Rodeo Drive shopping district, one of the most expensive in the world.

Business had declined significantly as smokers chose to dine across the city line at restaurants where they were allowed to puff away at will, said Rudy Cole, executive director of the Beverly Hills Restaurant Association.

Bob Spivak, the managing partner of The Grill, said Wednesday he was satisfied with the new rules.

''It's 9:30 in the morning,'' Spivak said. ''Our phones have only been open for half-an-hour and we've already had three calls (from smokers) to congratulate us and make reservations.''

David Zwaaf, president of the Rangoon Racquet Club, said the City Council ''clearly had a duty to protect not only the health of non-smokers, but also the economic health of the merchants who support this city.''

''The unfortunate thing is that even though this will bring in our smoking clientele, it's going to take a while to get them back,'' he said.

Zwaaf declined to specify the percentage dropoff in his business, characterizing it only as substantial. But he emphasized that operating a restaurant is not a high net-profit business.

''Even a 5 percent loss in gross revenues can mean a 30 percent loss in net profit,'' Zwaaf said.

Some council members said they changed their stance largely because many people were ignoring the original ordinance, which depended on restaurant patrons to make citizen's arrests of offending smokers.

''When we established this ordinance, we didn't mean to be pioneers,'' said Vice Mayor Donna Ellman. ''But when Beverly Hills speaks, the nation listens. Unfortunately, we didn't speak well. The ordinance was poorly drafted. There was, in effect, no ban at all - just lip service.''

Responsibility for enforcement now falls upon the restaurants' owners and managers, who will be required to deny service to patrons who light up outside designated non-smoking areas.

''This is not a step back. It's a step forward,'' Mayor Benjamin Stansbury declared. ''We can guarantee smoke-free environments.''