When it comes to air quality, Tokyo is the first and the last.

The capital's congested streets and its consistent failure to meet government-set standards make it the biggest target for increased administrative attention if its air quality is to improve.

It is also the only major urban area without a court verdict mandating that its government combat air pollution caused by motor vehicles.

But this could soon change.

On Dec. 18, plaintiffs suing the central and metropolitan governments, Metropolitan Expressway Public Corp., and seven automakers for the dismal air quality in Tokyo made their closing arguments in the Tokyo District Court, punctuating a historic battle that has lasted more than 5 1/2 years.

The 518 plaintiffs -- 45 of whom have died since the case went to court in May 1996 -- and their families contend that poor air quality in the Tokyo metropolitan area which has been spawned by administrative and manufacturing negligence has caused them serious respiratory illness and suffering.

They are seeking 11.7 billion yen in compensation and a court order that would force the central and local governments to crack down on pollution.

They are also asking that the state create a system to certify victims of air pollution in Tokyo and that a fund sponsored by manufacturers of diesel automobiles be established to shoulder their medical costs.

"The way things are now, there are people from the same area with the same illness from the same cause and some are certified as victims and get their medical bills paid while others don't," said Takuya Asano, a 39-year-old plaintiff and Koto Ward resident. "It is systemic discrimination."

A native of Hokkaido, Asano moved to Tokyo in 1987, a year before an air pollution compensation system was scrapped. He started suffering from serious respiratory ailments in the mid 1990s, he said.

"Look at me. I can't climb stairs. I have to carry this oxygen tank everywhere I go," shouted Asano in a meeting with Environment Ministry officials after the final court session.

Flanked by around 100 other plaintiffs and family members, Asano said that doctors told have him not to subject himself to any strain, because he could die.

His illness has kept him from working, and he has been hospitalized for months, lumbered with a medical bill of 400,000 yen and driven to the brink of suicide, he said.

In emotional testimonies, others claimed that their respiratory problems had cost them their jobs, and often, their families.

While there are no statistics available for adults, those for minors suggest the number of people afflicted with respiratory problems in Tokyo has risen every year since 1988.

In 1988 the government scrapped a system that provided certified victims of air pollution in 41 areas around the nation with support. It determined that air quality levels -- especially with regard to sulfur oxides -- had improved to such a degree that the system was no longer warranted, according to Hiroyuki Eguchi of the Environment Ministry.

"The air pollution situation changed from when the system was established (in 1974) and 1988," said Eguchi.

"Concentrations of sulfur oxides, which had been a problem, improved due to tougher regulations and industry efforts."

But while sulfur oxide levels may be under control, it is generally recognized that nitrous oxides, which interact with sunlight to form smog, and particulate matter -- the black, sooty residue belched from diesel-fueled machines -- remain at unhealthy levels.

Last year, an advisory group conducting a risk assessment of particulate matter, which can enter the lungs, said it is very likely carcinogenic. The ministry is performing tests on particulate matter, but the results will not be released for five years.

In addition, the ministry has secured 251 million yen from the fiscal 2002 budget to review measures regarding the substance and another 70 million yen to upgrade its measuring methods.

Environment Ministry officials concede that particulate matter probably causes cancer, impairs respiration to some degree, and increases mortality rates among the elderly when concentrations rise. They deny, however, that it causes asthma or chronic bronchitis.

"We are not saying any specific substance is responsible. It is a combination. What we are seeking is that the court order air quality be improved," said lawyer Kiyomi Hara, who represents Asano and the other plaintiffs.

If the plaintiffs win, the case could have weighty implications stretching beyond the health of those involved.

For one thing, it could greatly affect the air quality in Tokyo.

Any judgment that finds fault with the local and central governments and auto industry could raise the bar above past judgments that mandated stiff measures be taken to improve air quality.

Specifically, plaintiffs are hoping the government will rethink its road building policies and emissions standards, whether this means implementing new technologies or reducing auto production.

This could prove an expensive proposition for the auto industry.

The seven diesel automobile manufacturers named in the case could be found negligent for not equipping their products with available but expensive pollution reduction technology, such as computers that enhance combustion efficiency.

If found culpable, they could find themselves footing the medical bills for thousands of Tokyo residents. This in turn could lead to similar developments in other cities.

Finally, should the judge side with the plaintiffs' claim that air pollution is so pervasive that it affects everyone in the capital, it could open the door for claims from throughout Tokyo. This would be a first, breaking air pollution precedents in Amagasaki, Hyogo Prefecture, and Nagoya that limited claims to a prescribed area of roads.

The scientific jury is still out on the hazards of diesel particulate matter and other pollutants produced by motor vehicles. But Yoshio Shigeno argues that, for those with respiratory ailments, it is more about the everyday reality of paying medical bills and making ends meet than scientific data and correlative relationships unearthed by scientists in lab coats or bureaucrats in neckties.

"We need money for medical expenses. Many of these people force themselves to work, even though they are ill, just to pay bills. Even if you don't consider paying compensation, I ask that you set up a system for covering our medical expenses immediately," an emotional Shigeno told the ministry officials.

Shigeno has been attending the negotiations in lieu of his 57-year-old wife, who has been hospitalized for respiratory-related problems.

But whether the government and the automakers in question will be forced to take notice of his and others' impassioned pleas won't be known until next summer at the earliest, when the court is expected to announce its verdict.

Until then they will just have to hold their collective breath.