Local residents will see the impact of the new Clean Air Act in their electric bills, at the gas pump and on public buses. Whether they also will see smog-free skies is a question whose answer is years away.

Under the law signed yesterday by President Bush, the Washington area is on a list of seriously polluted areas that have until 1999 to meet federal smog standards. The area also must lower its unhealthy levels of carbon monoxide.

"There are three words for this area: cars, cars, cars," said Ed Barks, spokesman for the National Clean Air Coalition, an association of environmental groups.

Because Washington has few smokestack industries or power plants, the area's major cause of summer smog and winter carbon monoxide is the automobile -- the major target of the law's requirements here. That means cleaner-running cars, cleaner-burning fuel, new nozzles to trap vapors at suburban gas pumps, tighter inspection requirements and more encouragement to use mass transit.

The law imposes some specific mandates, but lets local and state officials plan additional steps, subject to federal approval. For the first time, however, Virginia, Maryland and the District may be required to go beyond cleaning local air and take additional steps to prevent pollution from drifting to Northeast states.

Other provisions with a local impact include:

Higher utility costs. Because utilities must reduce their use of high-sulfur coal, which has been linked to acid rain, Virginia Power says the typical customer, with a monthly bill of $79.83 for 1,000 kilowatts, could pay up to $5.60 more a month. The Potomac Electric Power Co. says consumers will have to help defray hundreds of millions of dollars in additional costs. Environmentalists differ, however, saying Virginia customers should have to pay 50 cents a month more, Maryland and District customers $2.10.

Metro and other bus companies must buy cleaner-running buses by the middle of the decade, which could cost millions on the heels of a period when fares already are rising to pay for other needs.

Tighter controls will be imposed on businesses such as bakeries, dry cleaners and printing plants. The good news: "We project little if any increase in price," said William Fisher, vice president of the International Fabricare Institute, a dry cleaning trade group.

Centrally fueled fleets -- such as groups of delivery vehicles -- may be required to burn cleaner fuels, such as natural gas.

Environmental groups, the American Lung Association and some local officials say the law may prevent local air from deterioriating, but will do little to improve it before the end of the decade. Even then, some say, the region's air still may not meet federal standards, because the bill's car provisions may not be tough enough to offset growth in traffic.

In the summer, cars spew out hydrocarbons and nitrogen oxides that bake in the sun to form low-level ozone, also known as smog, a nose and eye irritant that can cause lung damage. In the winter, other car emissions react with cold air to form carbon monoxide, which aggravates heart problems and can cause other health problems.

The new law requires cleaner-burning cars to be sold nationwide by 1996, but the American Lung Association says it will push the District, Maryland and Virginia to adopt California's more stringent standards for new cars sold locally. Cars meeting the California standards could cut output of some contaminants in half, the lung group says, while adding $100 to the cost of a car. Critics say the cost increase would be more like several hundred dollars.

Within four years, the new law will require gasoline stations in Washington area suburbs to install nozzles on their pumps to trap smog-causing vapors, which also have been linked to cancer. District stations already have such nozzles, but Maryland and Virginia officials have resisted.

Amoco Corp. is planning to install a new type of vapor-trapping nozzle, which officials say is as easy to use as a regular pump, at its 49 District stations by early next year. But Amoco and other oil companies are not rushing to add the nozzles in the suburbs before they are required to under the law. The equipment is estimated to add a penny or two to the price of each gallon of gasoline.

The new law requires sale of oxygenated fuel by 1992 in areas, including Washington, that have carbon monoxide problems. Amoco and Exxon Corp. announced this month that a blend is on sale locally now, partly because of customer demand. The firms say the marketplace will determine whether dealers charge more for the cleaner gasoline.

Owners of cars that fail state emissions tests now must spend $200 on repairs in Virginia and $75 in Maryland before they can obtain a waiver of the emissions requirement. That figure will rise to $450. In the District, the waiver cost is decided on a case-by-case basis.