A government study group on measures to reduce exhaust emissions from diesel-powered vehicles has compiled a midterm draft proposal calling for the replacement of older vehicles with new models, group sources said Tuesday.

The group -- made up of experts from the Transport Ministry, the International Trade and Industry Ministry and the Environment Agency -- proposed requiring owners of diesel vehicles manufactured in 1989 and before, when there were no emissions regulations, to replace their vehicles with new models, the sources said.

The study group had considered whether to require owners of all diesel-powered vehicles, regardless of when they were manufactured, to either install better mufflers with diesel particulate filters or to purchase new models, but decided an across-the-board application of that kind is not possible.

If the proposal to eliminate vehicles manufactured in 1989 and earlier is applied, some 80 percent of buses and about 70 percent of trucks currently in use nationwide would have to be replaced.

The Environment Agency is expected to include the kinds of vehicles subject to compulsory replacement in a draft bill on new emission controls it hopes to submit to the Diet next year, with the new regulations scheduled to take effect in 2002, the sources said.

The current law -- which covers Tokyo, Osaka and their vicinities -- took effect in late 1992 with the aim of reducing nitrogen oxide emissions by encouraging people to upgrade to cleaner vehicles.

The revisions are expected to cover emissions of particulate matter and broaden the targeted areas to include parts of Gunma and Tochigi prefectures, the cities of Nagoya, Kyoto and Fukuoka and their vicinities, the sources said.

Diesel pollutants are suspected of causing lung cancer and asthma, and of worsening hay fever and other allergies.

As of the end of fiscal 1999, there were a total of 4.81 million diesel-powered passenger cars in Japan, the agency said, adding that 48.6 percent of them were made in 1989 and before.

There are about 230,000 diesel buses, of which 78.6 percent were made in 1989 and before, and 6.33 million trucks, of which 68.7 percent were made in 1989 and before.