Pollution from automobiles in the Washington area is far worse than previously believed, and dramatic steps -- such as requiring the sale of methanol-fueled cars -- may be ordered to meet federal smog laws, according to local planning officials.

People are driving more miles than officials had estimated, mainly because they are taking more leisure trips than anticipated, adding to the pollution problem.

In addition, recent research shows cars produce twice the quantity of smog-causing chemicals as earlier thought, potentially adding more than 40 tons a day of pollution to the region's air. The pollutants come not from tailpipe exhaust, but from gasoline vapors that escape regardless of whether the car is running.

The dirty news is coming out as planners inventory the sources of area air pollution in preparation for writing a strategy to clean them up. The parameters and deadlines for that strategy will be contained in the clean air bill now being considered by a congressional conference committee.

"We're expecting, from the preliminary numbers we've seen, that the entire emissions inventory will show higher hydrocarbons . . . than we expected," said David Foerter, air quality planner for the Metropolitan Washington Council of Governments.

Smog is created when hydrocarbons and nitrogen oxides -- in this area, produced mainly by gasoline-powered cars and trucks -- cook in the sun and become ozone.

Unlike ozone in the stratosphere, which protects the planet from the sun's rays, this low-level ozone is a major lung irritant that can cause permanent health damage. On at least two days this summer, Washington's air quality reached unhealthy levels.

The clean air bill is likely to require that cars that cause less pollution be put on sale nationally, require power plants to clean up what is coming out of their smokestacks, encourage use of new gasoline formulas that emit fewer polluting vapors and require gasoline pumps in this region to have vapor-trapping nozzles, now already in place in the District.

Planners say the higher-than-expected local smog numbers may necessitate additional steps, although they say back-yard barbecues will not be restricted.

"I don't think we'll have to go to the extent they have in Los Angeles, but we'll have to look at changing lifestyles," said George Ferreri, Maryland's top air pollution official.

One step could be to mandate that a percentage of automobiles sold be fueled by gasoline alternatives such as methanol, perhaps starting with company-owned and government cars.

Baltimore, because it is so severely polluted, may be required to adopt that step under the new clean air legislation, and planners say it may be impractical to separate the Baltimore car market from the Washington market.

"I'm guessing out loud, but for Baltimore to do it by itself wouldn't be effective," Ferreri said. "It will have to be a little bit expanded."

Planners also may look at ways to persuade people to take fewer leisure trips, such as by improving bicycle paths or providing more public transit to shopping malls and entertainment.

Leisure trips account for two-thirds of the miles driven in this region, but have not been included in smog reduction plans because most are not made during rush hours.

The increase in car travel is outpacing employment and population growth for a variety of reasons -- longer commutes, more noontime errands because more women are in the work force, more vacation trips because of the recent economic boom.

The biggest surprise for planners when they compared estimates to actual driving was that "non-work travel was double what we had been expecting," said Michael Clifford, COG's chief transportation planner.

The unpleasant discovery about local air could have implications beyond the area, because pollution created in Washington drifts with the wind, pushing contamination into the already-smoggy Northeast states.

Federal research now underway indicates that the types of antipollution measures now included in proposed federal clean air legislation would not prevent smog violations from occurring along the 700-mile Virginia-to-Maine urban corridor.

William Becker, executive director of the State and Territorial Air Pollution Program Administrators, said federal officials believe regional emissions may need to be reduced by as much as 70 percent to meet smog standards.

"That's almost as much as Los Angeles needs in its program," he said. "It's a drastic reduction that would be required . . . that could tax the patience of the consumer."

Although Washington's air is cleaner than Baltimore's or New York's, Becker said this area will be pressured to take extra steps to help its northern neighbors.

Federal clean air legislation likely will create a regional air pollution district stretching from here to New England that could impose solutions on one area that is contributing to another area's smog.