The U.S. Environmental Protection Agency's proposed standards for fine particulate matter are tighter than the existing regulations, but weaker than a scientific board recommended and also not as stringent as the revisions recommended by EPA staff. Administrator Stephen L. Johnson announced the proposed restrictions Dec. 20 in a conference call with reporters.

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The proposed rules, which are subject to public comment and would take effect next year, are aimed at particles of 2.5 micrometers and less. The current annual average concentration lmit, 15 micrograms per cubic meter of air, would remain in effect. But EPA wants to ratchet down daily limits from 65 micrograms to 35 micrograms. Last June, EPA's Clean Air Scientific Advisory Committee, after reviewing some 2,000 health studies, recommended lowering the standard to a daily limit of 35 to 30 micrograms and an annual limit of 14 to 13 micrograms.

EPA's Johnson said he made the recommendation "based on the scientific evidence available." On the day the study was announced , however, new research bolstered the case linking particulate matter to heart disease, even at compliance levels.

The agency estimates that the new standards will push the nationwide level of counties in violation to 191, up from the current non-attainment level of 116.

Industry organizations point to progress made over the past three decades. The Electric Reliability Coordinating Council says that coal-fired powerplants are just now putting in place the last round of revisions from 1997. Environmental organizations and public health advocacy groups threatened to file more lawsuits to tighten the limits further.