The government Friday drastically revised standards for workplace exposure to hazardous materials, regulating 164 substances for the first time and reducing exposure limits for hundreds more in an action it said could prevent 700 deaths and 55,000 illnesses a year.

The new regulations, two years in the making, should significantly curtail the risk of illness to 21 million Americans who work in general industry and are potentially exposed to toxic and hazardous substances, the Labor Department said.Of that number, 4.5 million workers currently face exposure to hazardous materials at rates above the new limits, the department's Occupational Safety and Health Administration said in releasing the regulations, the first large-scale changes to exposure standards in nearly 20 years.

The changes should cost affected establishments an average of $6,000 a year each, the government said. Those costs would range from $77,400 a year for petroleum refineries to $360 annually for auto dealers. The average per-worker cost is $150.

The department considered the limits for more than 400 industrial chemicals and substances in a single review, departing from a policy of case-by-case study that had produced new, comprehensive standards for just 24 substances in the past 17 years.

"We were able to make a 20-year leap forward in the level of worker protection in a relatively short time," said John A. Pendergrass, the assistant labor secretary who heads OSHA. "We also have saved the American taxpayers tens of millions of dollars that otherwise would have been spent over a long period of time in individual rulemakings."

OSHA placed 164 substances under exposure limits for the first time, reduced allowable limits for 212 others and let stand existing limits on 52 substances. The new limits take effect March 1 and employers must be in compliance by Sept. 1. Exposure limits will remain unchanged for 169 additional substances not covered by the two-year review.