Even before the D.C. Council gives final approval to a measure that would ban smoking in bars and restaurants, advocates on both sides of the issue are clashing over which businesses would qualify for exemptions based on economic hardship.

The smoking ban, which won the council's preliminary approval in a 12 to 1 vote Tuesday, included a hardship exemption allowing the mayor to issue a waiver to businesses that can show the measure is causing them "undue financial hardship.'' Two council members who support the ban said that wording is vague and vowed to define the exemption as narrowly as possible before a final vote in the next few weeks.

"The waiver is so broad you can drive a tobacco truck through it," said council member Adrian M. Fenty (D-Ward 4), one of the ban's original proponents. He said he will offer an amendment that would exempt only bars and restaurants that can show a 15 percent or more decline in business compared with a year earlier. The smoking ban passed by New York State in July 2003 includes a hardship waiver based on a 15 percent drop in business.

Under the measure approved by the council, even if a venue were issued a waiver, smoking would be allowed in only 25 percent of the business area.

Mayor Anthony A. Williams (D) has resisted a smoking ban in past years, concerned that small businesses and neighborhood bars would be hurt. This year he indicated support for a New York-style ban, saying there was little evidence it would inflict economic pain. But he has said he opposes the ban approved Tuesday.

"Generally speaking, there should be some room for people who have a restaurant with a bar area to be exempted,'' said Vince Morris, a mayoral spokesman. Morris said it was difficult to predict whether the mayor will veto the bill because it might change substantially by the final vote.

Fenty said Williams's opposition to a comprehensive ban is another reason why the council, not the administration, should decide exactly what represents an economic hardship.

Council member David A. Catania (I-At Large), the author of the hardship exemption included in the measure, said the council should not micromanage the process. Instead, he said, the blanks should be filled in after the legislation is adopted, during a rule-making process that includes public input.

Catania said requirements for an exemption should be determined by the competitive and economic circumstances of District restaurants and bars, not by an arbitrary number plucked from another jurisdiction.

He said he expects exemptions to be as rare as they are in New York, where 50 of them have been approved since the ban took effect.

"There is no monkey business going on," Catania said. "This is not an exemption that swallows the rule."

The measure approved Tuesday prohibits smoking in bars, restaurants and other indoor public places, bringing the District closer to joining Boston and other cities. Chicago officials passed a smoking ban yesterday, but it allows smoking in bars until mid-2008. In the Washington area, Montgomery, Prince George's and Talbot counties have enacted smoking bans, and Howard County is considering one.

The District's smoke-free proposal is similar to New York's ban. It would include exemptions for outdoor areas, cigar bars, hotel rooms, retail tobacco outlets and facilities that research the effects of smoking. The measure would affect all restaurant eating areas immediately but would give bars, clubs, taverns and the bar areas of restaurants until January 2007 to go smoke-free.

Both sides are looking to New York's experience. Among the exemptions approved there include 13 for veterans halls and organizations such as the Loyal Order of Moose #1048 in Canandaigua. No exemptions have been approved for New York City venues, according to Jeffrey Hammond, a spokesman for the New York State Department of Health.

Council member Carol Schwartz (R-At Large), the fiercest opponent of a smoking ban on the council and the only member to vote against the measure, said a waiver would probably not save too many businesses.

"Most restaurants don't have that much of a profit margin anyway," she said. "By the time you recognize any economic hardship, you'll be out of business."

And she described the prospect of a business's successfully applying to the District government for relief as almost laughable.

"How many years will that take?" she said. "Please."

Trista Hargrove, a spokeswoman for the Cancer Action Network, part of the American Cancer Society, said her organization believes a waiver process is unnecessary.

"The waiver is based on the assumption that smoke-free laws hurt, when in fact the opposite is true, and we have dozens of scientific studies that show smoke free laws do not hurt or harm," she said.