The amount of pollution generated by traffic in the Washington region is far worse than previously believed, according to a new analysis by transportation planners who are concerned the problem could jeopardize road and transit projects.

Pollution experts at the Metropolitan Washington Council of Governments, a regional planning agency, were startled by the new figures indicating that the increase in sport-utility vehicles, pickups and diesel trucks would cause the region to exceed its limits on exhaust by 30 percent.

If the problem isn't solved by January 2004, when the current regional transportation plan expires, any road or transit projects not already under contract would not win federal approval. The region would first have to find a way to control the pollution, said Ronald F. Kirby, COG's transportation planning director.

Solving the problem won't come quickly or cheaply. It took Maryland, Virginia and the District a year of wrangling and a pledge of $42 million worth of clean-air programs to curtail excess emissions estimated at three tons a day. The new figures project a 50-ton-a-day problem.

"I was expecting double digits, but not as big an amount as this," Kirby said of the new figures. "We've got to find ways of getting these emissions down in relatively short order."

Kirby said the problem emerged recently when planners recalculated vehicle emissions using a new computer model required by the U.S. Environmental Protection Agency. It is more sensitive to the wide range of vehicles on the roads. For example, it differentiates between exhaust from a small SUV, like a Honda CRV, and a heavier one, like the Ford Expedition.

It also assumes, based on national data, that the percentage of miles driven in heavier, higher-polluting vehicles has increased by almost 20 percent since 1990.

Vehicle exhaust combines with sunlight to form unhealthy levels of ground-level ozone, which leads to the Code Red alerts that warn children, the elderly and people with asthma and other breathing problems to limit time outdoors.

Kirby said other large urban areas also are finding their new calculations higher than expected. When the air-quality standards were set, Kirby said, no one anticipated the popularity of SUVs or the growth in the number of trucks.

Regional officials who struggled to shrink the vehicle exhaust problem last year, when emissions were last calculated, said they were stunned at the new figures.

"My heart skipped a beat," said D.C. Council member Phil Mendelson (D-At Large), chairman of COG's Transportation Planning Board. "I thought it was going to be more like 15" tons over the limit, not 50.

"There's no way in the world the region is going to build any more major road projects in light of these results," said Loudoun County Supervisor James G. Burton (I-Mercer), a slow-growth proponent. "You can't solve this problem with the marginal solutions that have been put on the table for the last three or four years."

Melanie Mayock of the Sierra Club in Northern Virginia said she is concerned that the EPA will propose a loophole to help regions get around the problem.

"It shows we have a really big public health problem in this region because of air pollution," Mayock said. "It also shows we need smarter growth now."

The federal government requires regions such as Washington to impose restrictions on emissions from traffic, power plants, gas stations and other pollution sources as part of a plan to eventually meet federal clean-air standards. Under federal rules, the region has been in "serious" violation of ozone standards for years. After a review that preceded the new analysis, the EPA announced this week that it considers the region in "severe" violation.

Federal law allows three violations of ozone standards over a three-year period. This summer alone, the region had nine.

COG planners calculate future vehicle emissions using computer models that combine information, such as vehicle registrations and census data, with assumptions about how often and how far people drive. The region can offset high emissions by funding transit, encouraging telecommuting and providing other incentives for people to forgo driving. That's how the Washington region barely met its self-imposed limits on vehicle emissions this summer.

Fixing a 50-ton problem will take more than clean-air programs, officials said, largely because truck deliveries are an integral part of the economy. They said they will have to reconsider the region's entire clean-air plan, including the need for tighter controls on other emissions sources, such as power plants, construction equipment and lawn mowers.

"I think almost everything is going to have to be on the table," said Katherine K. Hanley (D), chairman of the Fairfax County Board of Supervisors and head of the region's air quality committee.

Kirby said the new findings are preliminary but within 5 to 10 percent of what the final figures are likely to be. They will be presented to the Transportation Planning Board on Wednesday.

Staff writer Michael Laris contributed to this report.